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rocksdb/utilities/transactions/optimistic_transaction_test.cc

1431 lines
42 KiB

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#ifndef ROCKSDB_LITE
#include <functional>
#include <string>
#include <thread>
#include "db/db_impl/db_impl.h"
#include "db/db_test_util.h"
#include "port/port.h"
#include "rocksdb/db.h"
#include "rocksdb/perf_context.h"
#include "rocksdb/utilities/optimistic_transaction_db.h"
#include "rocksdb/utilities/transaction.h"
#include "test_util/sync_point.h"
#include "test_util/testharness.h"
#include "test_util/transaction_test_util.h"
#include "util/crc32c.h"
#include "util/random.h"
namespace ROCKSDB_NAMESPACE {
class OptimisticTransactionTest
: public testing::Test,
public testing::WithParamInterface<OccValidationPolicy> {
public:
OptimisticTransactionDB* txn_db;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string dbname;
Options options;
OptimisticTransactionTest() {
options.create_if_missing = true;
options.max_write_buffer_number = 2;
options.max_write_buffer_size_to_maintain = 2 * Arena::kInlineSize;
options.merge_operator.reset(new TestPutOperator());
dbname = test::PerThreadDBPath("optimistic_transaction_testdb");
DestroyDB(dbname, options);
Open();
}
~OptimisticTransactionTest() override {
delete txn_db;
DestroyDB(dbname, options);
}
void Reopen() {
delete txn_db;
txn_db = nullptr;
Open();
}
private:
void Open() {
ColumnFamilyOptions cf_options(options);
OptimisticTransactionDBOptions occ_opts;
occ_opts.validate_policy = GetParam();
std::vector<ColumnFamilyDescriptor> column_families;
std::vector<ColumnFamilyHandle*> handles;
column_families.push_back(
ColumnFamilyDescriptor(kDefaultColumnFamilyName, cf_options));
Status s =
OptimisticTransactionDB::Open(DBOptions(options), occ_opts, dbname,
column_families, &handles, &txn_db);
ASSERT_OK(s);
ASSERT_NE(txn_db, nullptr);
ASSERT_EQ(handles.size(), 1);
delete handles[0];
}
};
TEST_P(OptimisticTransactionTest, SuccessTest) {
WriteOptions write_options;
ReadOptions read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, Slice("foo"), Slice("bar")));
ASSERT_OK(txn_db->Put(write_options, Slice("foo2"), Slice("bar")));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
ASSERT_OK(txn->GetForUpdate(read_options, "foo", &value));
ASSERT_EQ(value, "bar");
ASSERT_OK(txn->Put(Slice("foo"), Slice("bar2")));
ASSERT_OK(txn->GetForUpdate(read_options, "foo", &value));
ASSERT_EQ(value, "bar2");
ASSERT_OK(txn->Commit());
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "bar2");
delete txn;
}
TEST_P(OptimisticTransactionTest, WriteConflictTest) {
WriteOptions write_options;
ReadOptions read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, "foo", "bar"));
ASSERT_OK(txn_db->Put(write_options, "foo2", "bar"));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
ASSERT_OK(txn->Put("foo", "bar2"));
// This Put outside of a transaction will conflict with the previous write
ASSERT_OK(txn_db->Put(write_options, "foo", "barz"));
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "barz");
ASSERT_EQ(1, txn->GetNumKeys());
Status s = txn->Commit();
ASSERT_TRUE(s.IsBusy()); // Txn should not commit
// Verify that transaction did not write anything
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "barz");
ASSERT_OK(txn_db->Get(read_options, "foo2", &value));
ASSERT_EQ(value, "bar");
delete txn;
}
TEST_P(OptimisticTransactionTest, WriteConflictTest2) {
WriteOptions write_options;
ReadOptions read_options;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, "foo", "bar"));
ASSERT_OK(txn_db->Put(write_options, "foo2", "bar"));
txn_options.set_snapshot = true;
Transaction* txn = txn_db->BeginTransaction(write_options, txn_options);
ASSERT_NE(txn, nullptr);
// This Put outside of a transaction will conflict with a later write
ASSERT_OK(txn_db->Put(write_options, "foo", "barz"));
ASSERT_OK(txn->Put(
"foo", "bar2")); // Conflicts with write done after snapshot taken
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "barz");
Status s = txn->Commit();
ASSERT_TRUE(s.IsBusy()); // Txn should not commit
// Verify that transaction did not write anything
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "barz");
ASSERT_OK(txn_db->Get(read_options, "foo2", &value));
ASSERT_EQ(value, "bar");
delete txn;
}
TEST_P(OptimisticTransactionTest, ReadConflictTest) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, "foo", "bar"));
ASSERT_OK(txn_db->Put(write_options, "foo2", "bar"));
txn_options.set_snapshot = true;
Transaction* txn = txn_db->BeginTransaction(write_options, txn_options);
ASSERT_NE(txn, nullptr);
txn->SetSnapshot();
snapshot_read_options.snapshot = txn->GetSnapshot();
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "foo", &value));
ASSERT_EQ(value, "bar");
// This Put outside of a transaction will conflict with the previous read
ASSERT_OK(txn_db->Put(write_options, "foo", "barz"));
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "barz");
Status s = txn->Commit();
ASSERT_TRUE(s.IsBusy()); // Txn should not commit
// Verify that transaction did not write anything
ASSERT_OK(txn->GetForUpdate(read_options, "foo", &value));
ASSERT_EQ(value, "barz");
ASSERT_OK(txn->GetForUpdate(read_options, "foo2", &value));
ASSERT_EQ(value, "bar");
delete txn;
}
TEST_P(OptimisticTransactionTest, TxnOnlyTest) {
// Test to make sure transactions work when there are no other writes in an
// empty db.
WriteOptions write_options;
ReadOptions read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
ASSERT_OK(txn->Put("x", "y"));
ASSERT_OK(txn->Commit());
delete txn;
}
TEST_P(OptimisticTransactionTest, FlushTest) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, Slice("foo"), Slice("bar")));
ASSERT_OK(txn_db->Put(write_options, Slice("foo2"), Slice("bar")));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
snapshot_read_options.snapshot = txn->GetSnapshot();
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "foo", &value));
ASSERT_EQ(value, "bar");
ASSERT_OK(txn->Put(Slice("foo"), Slice("bar2")));
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "foo", &value));
ASSERT_EQ(value, "bar2");
// Put a random key so we have a memtable to flush
ASSERT_OK(txn_db->Put(write_options, "dummy", "dummy"));
// force a memtable flush
FlushOptions flush_ops;
ASSERT_OK(txn_db->Flush(flush_ops));
// txn should commit since the flushed table is still in MemtableList History
ASSERT_OK(txn->Commit());
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "bar2");
delete txn;
}
TEST_P(OptimisticTransactionTest, FlushTest2) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, Slice("foo"), Slice("bar")));
ASSERT_OK(txn_db->Put(write_options, Slice("foo2"), Slice("bar")));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
snapshot_read_options.snapshot = txn->GetSnapshot();
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "foo", &value));
ASSERT_EQ(value, "bar");
ASSERT_OK(txn->Put(Slice("foo"), Slice("bar2")));
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "foo", &value));
ASSERT_EQ(value, "bar2");
// Put a random key so we have a MemTable to flush
ASSERT_OK(txn_db->Put(write_options, "dummy", "dummy"));
// force a memtable flush
FlushOptions flush_ops;
ASSERT_OK(txn_db->Flush(flush_ops));
// Put a random key so we have a MemTable to flush
ASSERT_OK(txn_db->Put(write_options, "dummy", "dummy2"));
// force a memtable flush
ASSERT_OK(txn_db->Flush(flush_ops));
ASSERT_OK(txn_db->Put(write_options, "dummy", "dummy3"));
// force a memtable flush
// Since our test db has max_write_buffer_number=2, this flush will cause
// the first memtable to get purged from the MemtableList history.
ASSERT_OK(txn_db->Flush(flush_ops));
Status s = txn->Commit();
// txn should not commit since MemTableList History is not large enough
ASSERT_TRUE(s.IsTryAgain());
ASSERT_OK(txn_db->Get(read_options, "foo", &value));
ASSERT_EQ(value, "bar");
delete txn;
}
// Trigger the condition where some old memtables are skipped when doing
// TransactionUtil::CheckKey(), and make sure the result is still correct.
TEST_P(OptimisticTransactionTest, CheckKeySkipOldMemtable) {
const int kAttemptHistoryMemtable = 0;
const int kAttemptImmMemTable = 1;
for (int attempt = kAttemptHistoryMemtable; attempt <= kAttemptImmMemTable;
attempt++) {
Reopen();
WriteOptions write_options;
ReadOptions read_options;
ReadOptions snapshot_read_options;
ReadOptions snapshot_read_options2;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, Slice("foo"), Slice("bar")));
ASSERT_OK(txn_db->Put(write_options, Slice("foo2"), Slice("bar")));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_TRUE(txn != nullptr);
Transaction* txn2 = txn_db->BeginTransaction(write_options);
ASSERT_TRUE(txn2 != nullptr);
snapshot_read_options.snapshot = txn->GetSnapshot();
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "foo", &value));
ASSERT_EQ(value, "bar");
ASSERT_OK(txn->Put(Slice("foo"), Slice("bar2")));
snapshot_read_options2.snapshot = txn2->GetSnapshot();
ASSERT_OK(txn2->GetForUpdate(snapshot_read_options2, "foo2", &value));
ASSERT_EQ(value, "bar");
ASSERT_OK(txn2->Put(Slice("foo2"), Slice("bar2")));
// txn updates "foo" and txn2 updates "foo2", and now a write is
// issued for "foo", which conflicts with txn but not txn2
ASSERT_OK(txn_db->Put(write_options, "foo", "bar"));
if (attempt == kAttemptImmMemTable) {
// For the second attempt, hold flush from beginning. The memtable
// will be switched to immutable after calling TEST_SwitchMemtable()
// while CheckKey() is called.
ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->LoadDependency(
{{"OptimisticTransactionTest.CheckKeySkipOldMemtable",
"FlushJob::Start"}});
ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->EnableProcessing();
}
// force a memtable flush. The memtable should still be kept
FlushOptions flush_ops;
if (attempt == kAttemptHistoryMemtable) {
ASSERT_OK(txn_db->Flush(flush_ops));
} else {
ASSERT_EQ(attempt, kAttemptImmMemTable);
DBImpl* db_impl = static_cast<DBImpl*>(txn_db->GetRootDB());
ASSERT_OK(db_impl->TEST_SwitchMemtable());
}
uint64_t num_imm_mems;
ASSERT_TRUE(txn_db->GetIntProperty(DB::Properties::kNumImmutableMemTable,
&num_imm_mems));
if (attempt == kAttemptHistoryMemtable) {
ASSERT_EQ(0, num_imm_mems);
} else {
ASSERT_EQ(attempt, kAttemptImmMemTable);
ASSERT_EQ(1, num_imm_mems);
}
// Put something in active memtable
ASSERT_OK(txn_db->Put(write_options, Slice("foo3"), Slice("bar")));
// Create txn3 after flushing, when this transaction is commited,
// only need to check the active memtable
Transaction* txn3 = txn_db->BeginTransaction(write_options);
ASSERT_TRUE(txn3 != nullptr);
// Commit both of txn and txn2. txn will conflict but txn2 will
// pass. In both ways, both memtables are queried.
SetPerfLevel(PerfLevel::kEnableCount);
get_perf_context()->Reset();
Status s = txn->Commit();
// We should have checked two memtables
ASSERT_EQ(2, get_perf_context()->get_from_memtable_count);
// txn should fail because of conflict, even if the memtable
// has flushed, because it is still preserved in history.
ASSERT_TRUE(s.IsBusy());
get_perf_context()->Reset();
s = txn2->Commit();
// We should have checked two memtables
ASSERT_EQ(2, get_perf_context()->get_from_memtable_count);
ASSERT_TRUE(s.ok());
ASSERT_OK(txn3->Put(Slice("foo2"), Slice("bar2")));
get_perf_context()->Reset();
s = txn3->Commit();
// txn3 is created after the active memtable is created, so that is the only
// memtable to check.
ASSERT_EQ(1, get_perf_context()->get_from_memtable_count);
ASSERT_TRUE(s.ok());
TEST_SYNC_POINT("OptimisticTransactionTest.CheckKeySkipOldMemtable");
ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->DisableProcessing();
SetPerfLevel(PerfLevel::kDisable);
delete txn;
delete txn2;
delete txn3;
}
}
TEST_P(OptimisticTransactionTest, NoSnapshotTest) {
WriteOptions write_options;
ReadOptions read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, "AAA", "bar"));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
// Modify key after transaction start
ASSERT_OK(txn_db->Put(write_options, "AAA", "bar1"));
// Read and write without a snapshot
ASSERT_OK(txn->GetForUpdate(read_options, "AAA", &value));
ASSERT_EQ(value, "bar1");
ASSERT_OK(txn->Put("AAA", "bar2"));
// Should commit since read/write was done after data changed
ASSERT_OK(txn->Commit());
ASSERT_OK(txn->GetForUpdate(read_options, "AAA", &value));
ASSERT_EQ(value, "bar2");
delete txn;
}
TEST_P(OptimisticTransactionTest, MultipleSnapshotTest) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, "AAA", "bar"));
ASSERT_OK(txn_db->Put(write_options, "BBB", "bar"));
ASSERT_OK(txn_db->Put(write_options, "CCC", "bar"));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
ASSERT_OK(txn_db->Put(write_options, "AAA", "bar1"));
// Read and write without a snapshot
ASSERT_OK(txn->GetForUpdate(read_options, "AAA", &value));
ASSERT_EQ(value, "bar1");
ASSERT_OK(txn->Put("AAA", "bar2"));
// Modify BBB before snapshot is taken
ASSERT_OK(txn_db->Put(write_options, "BBB", "bar1"));
txn->SetSnapshot();
snapshot_read_options.snapshot = txn->GetSnapshot();
// Read and write with snapshot
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "BBB", &value));
ASSERT_EQ(value, "bar1");
ASSERT_OK(txn->Put("BBB", "bar2"));
ASSERT_OK(txn_db->Put(write_options, "CCC", "bar1"));
// Set a new snapshot
txn->SetSnapshot();
snapshot_read_options.snapshot = txn->GetSnapshot();
// Read and write with snapshot
ASSERT_OK(txn->GetForUpdate(snapshot_read_options, "CCC", &value));
ASSERT_EQ(value, "bar1");
ASSERT_OK(txn->Put("CCC", "bar2"));
ASSERT_OK(txn->GetForUpdate(read_options, "AAA", &value));
ASSERT_EQ(value, "bar2");
ASSERT_OK(txn->GetForUpdate(read_options, "BBB", &value));
ASSERT_EQ(value, "bar2");
ASSERT_OK(txn->GetForUpdate(read_options, "CCC", &value));
ASSERT_EQ(value, "bar2");
ASSERT_OK(txn_db->Get(read_options, "AAA", &value));
ASSERT_EQ(value, "bar1");
ASSERT_OK(txn_db->Get(read_options, "BBB", &value));
ASSERT_EQ(value, "bar1");
ASSERT_OK(txn_db->Get(read_options, "CCC", &value));
ASSERT_EQ(value, "bar1");
ASSERT_OK(txn->Commit());
ASSERT_OK(txn_db->Get(read_options, "AAA", &value));
ASSERT_EQ(value, "bar2");
ASSERT_OK(txn_db->Get(read_options, "BBB", &value));
ASSERT_EQ(value, "bar2");
ASSERT_OK(txn_db->Get(read_options, "CCC", &value));
ASSERT_EQ(value, "bar2");
// verify that we track multiple writes to the same key at different snapshots
delete txn;
txn = txn_db->BeginTransaction(write_options);
// Potentially conflicting writes
ASSERT_OK(txn_db->Put(write_options, "ZZZ", "zzz"));
ASSERT_OK(txn_db->Put(write_options, "XXX", "xxx"));
txn->SetSnapshot();
OptimisticTransactionOptions txn_options;
txn_options.set_snapshot = true;
Transaction* txn2 = txn_db->BeginTransaction(write_options, txn_options);
txn2->SetSnapshot();
// This should not conflict in txn since the snapshot is later than the
// previous write (spoiler alert: it will later conflict with txn2).
ASSERT_OK(txn->Put("ZZZ", "zzzz"));
ASSERT_OK(txn->Commit());
delete txn;
// This will conflict since the snapshot is earlier than another write to ZZZ
ASSERT_OK(txn2->Put("ZZZ", "xxxxx"));
Status s = txn2->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn2;
}
TEST_P(OptimisticTransactionTest, ColumnFamiliesTest) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ColumnFamilyHandle *cfa, *cfb;
ColumnFamilyOptions cf_options;
// Create 2 new column families
ASSERT_OK(txn_db->CreateColumnFamily(cf_options, "CFA", &cfa));
ASSERT_OK(txn_db->CreateColumnFamily(cf_options, "CFB", &cfb));
delete cfa;
delete cfb;
delete txn_db;
txn_db = nullptr;
// open DB with three column families
std::vector<ColumnFamilyDescriptor> column_families;
// have to open default column family
column_families.push_back(
ColumnFamilyDescriptor(kDefaultColumnFamilyName, ColumnFamilyOptions()));
// open the new column families
column_families.push_back(
ColumnFamilyDescriptor("CFA", ColumnFamilyOptions()));
column_families.push_back(
ColumnFamilyDescriptor("CFB", ColumnFamilyOptions()));
std::vector<ColumnFamilyHandle*> handles;
ASSERT_OK(OptimisticTransactionDB::Open(options, dbname, column_families,
&handles, &txn_db));
assert(txn_db != nullptr);
ASSERT_NE(txn_db, nullptr);
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
txn->SetSnapshot();
snapshot_read_options.snapshot = txn->GetSnapshot();
txn_options.set_snapshot = true;
Transaction* txn2 = txn_db->BeginTransaction(write_options, txn_options);
ASSERT_TRUE(txn2);
// Write some data to the db
WriteBatch batch;
ASSERT_OK(batch.Put("foo", "foo"));
ASSERT_OK(batch.Put(handles[1], "AAA", "bar"));
ASSERT_OK(batch.Put(handles[1], "AAAZZZ", "bar"));
ASSERT_OK(txn_db->Write(write_options, &batch));
ASSERT_OK(txn_db->Delete(write_options, handles[1], "AAAZZZ"));
// These keys do no conflict with existing writes since they're in
// different column families
ASSERT_OK(txn->Delete("AAA"));
Status s =
txn->GetForUpdate(snapshot_read_options, handles[1], "foo", &value);
ASSERT_TRUE(s.IsNotFound());
Slice key_slice("AAAZZZ");
Slice value_slices[2] = {Slice("bar"), Slice("bar")};
ASSERT_OK(txn->Put(handles[2], SliceParts(&key_slice, 1),
SliceParts(value_slices, 2)));
ASSERT_EQ(3, txn->GetNumKeys());
// Txn should commit
ASSERT_OK(txn->Commit());
s = txn_db->Get(read_options, "AAA", &value);
ASSERT_TRUE(s.IsNotFound());
s = txn_db->Get(read_options, handles[2], "AAAZZZ", &value);
ASSERT_EQ(value, "barbar");
Slice key_slices[3] = {Slice("AAA"), Slice("ZZ"), Slice("Z")};
Slice value_slice("barbarbar");
// This write will cause a conflict with the earlier batch write
ASSERT_OK(txn2->Put(handles[1], SliceParts(key_slices, 3),
SliceParts(&value_slice, 1)));
ASSERT_OK(txn2->Delete(handles[2], "XXX"));
ASSERT_OK(txn2->Delete(handles[1], "XXX"));
s = txn2->GetForUpdate(snapshot_read_options, handles[1], "AAA", &value);
ASSERT_TRUE(s.IsNotFound());
// Verify txn did not commit
s = txn2->Commit();
ASSERT_TRUE(s.IsBusy());
s = txn_db->Get(read_options, handles[1], "AAAZZZ", &value);
ASSERT_TRUE(s.IsNotFound());
ASSERT_EQ(value, "barbar");
delete txn;
delete txn2;
txn = txn_db->BeginTransaction(write_options, txn_options);
snapshot_read_options.snapshot = txn->GetSnapshot();
txn2 = txn_db->BeginTransaction(write_options, txn_options);
ASSERT_NE(txn, nullptr);
std::vector<ColumnFamilyHandle*> multiget_cfh = {handles[1], handles[2],
handles[0], handles[2]};
std::vector<Slice> multiget_keys = {"AAA", "AAAZZZ", "foo", "foo"};
std::vector<std::string> values(4);
std::vector<Status> results = txn->MultiGetForUpdate(
snapshot_read_options, multiget_cfh, multiget_keys, &values);
ASSERT_OK(results[0]);
ASSERT_OK(results[1]);
ASSERT_OK(results[2]);
ASSERT_TRUE(results[3].IsNotFound());
ASSERT_EQ(values[0], "bar");
ASSERT_EQ(values[1], "barbar");
ASSERT_EQ(values[2], "foo");
ASSERT_OK(txn->Delete(handles[2], "ZZZ"));
ASSERT_OK(txn->Put(handles[2], "ZZZ", "YYY"));
ASSERT_OK(txn->Put(handles[2], "ZZZ", "YYYY"));
ASSERT_OK(txn->Delete(handles[2], "ZZZ"));
ASSERT_OK(txn->Put(handles[2], "AAAZZZ", "barbarbar"));
ASSERT_EQ(5, txn->GetNumKeys());
// Txn should commit
ASSERT_OK(txn->Commit());
s = txn_db->Get(read_options, handles[2], "ZZZ", &value);
ASSERT_TRUE(s.IsNotFound());
// Put a key which will conflict with the next txn using the previous snapshot
ASSERT_OK(txn_db->Put(write_options, handles[2], "foo", "000"));
results = txn2->MultiGetForUpdate(snapshot_read_options, multiget_cfh,
multiget_keys, &values);
ASSERT_OK(results[0]);
ASSERT_OK(results[1]);
ASSERT_OK(results[2]);
ASSERT_TRUE(results[3].IsNotFound());
ASSERT_EQ(values[0], "bar");
ASSERT_EQ(values[1], "barbar");
ASSERT_EQ(values[2], "foo");
// Verify Txn Did not Commit
s = txn2->Commit();
ASSERT_TRUE(s.IsBusy());
s = txn_db->DropColumnFamily(handles[1]);
ASSERT_OK(s);
s = txn_db->DropColumnFamily(handles[2]);
ASSERT_OK(s);
delete txn;
delete txn2;
for (auto handle : handles) {
delete handle;
}
}
TEST_P(OptimisticTransactionTest, EmptyTest) {
WriteOptions write_options;
ReadOptions read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, "aaa", "aaa"));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn->Commit());
delete txn;
txn = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn->Rollback());
delete txn;
txn = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn->GetForUpdate(read_options, "aaa", &value));
ASSERT_EQ(value, "aaa");
ASSERT_OK(txn->Commit());
delete txn;
txn = txn_db->BeginTransaction(write_options);
txn->SetSnapshot();
ASSERT_OK(txn->GetForUpdate(read_options, "aaa", &value));
ASSERT_EQ(value, "aaa");
ASSERT_OK(txn_db->Put(write_options, "aaa", "xxx"));
Status s = txn->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn;
}
TEST_P(OptimisticTransactionTest, PredicateManyPreceders) {
WriteOptions write_options;
ReadOptions read_options1, read_options2;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
txn_options.set_snapshot = true;
Transaction* txn1 = txn_db->BeginTransaction(write_options, txn_options);
read_options1.snapshot = txn1->GetSnapshot();
Transaction* txn2 = txn_db->BeginTransaction(write_options);
txn2->SetSnapshot();
read_options2.snapshot = txn2->GetSnapshot();
std::vector<Slice> multiget_keys = {"1", "2", "3"};
std::vector<std::string> multiget_values;
std::vector<Status> results =
txn1->MultiGetForUpdate(read_options1, multiget_keys, &multiget_values);
ASSERT_TRUE(results[0].IsNotFound());
ASSERT_TRUE(results[1].IsNotFound());
ASSERT_TRUE(results[2].IsNotFound());
ASSERT_OK(txn2->Put("2", "x"));
ASSERT_OK(txn2->Commit());
multiget_values.clear();
results =
txn1->MultiGetForUpdate(read_options1, multiget_keys, &multiget_values);
ASSERT_TRUE(results[0].IsNotFound());
ASSERT_TRUE(results[1].IsNotFound());
ASSERT_TRUE(results[2].IsNotFound());
// should not commit since txn2 wrote a key txn has read
Status s = txn1->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
delete txn2;
txn1 = txn_db->BeginTransaction(write_options, txn_options);
read_options1.snapshot = txn1->GetSnapshot();
txn2 = txn_db->BeginTransaction(write_options, txn_options);
read_options2.snapshot = txn2->GetSnapshot();
ASSERT_OK(txn1->Put("4", "x"));
ASSERT_OK(txn2->Delete("4"));
// txn1 can commit since txn2's delete hasn't happened yet (it's just batched)
ASSERT_OK(txn1->Commit());
s = txn2->GetForUpdate(read_options2, "4", &value);
ASSERT_TRUE(s.IsNotFound());
// txn2 cannot commit since txn1 changed "4"
s = txn2->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
delete txn2;
}
TEST_P(OptimisticTransactionTest, LostUpdate) {
WriteOptions write_options;
ReadOptions read_options, read_options1, read_options2;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
// Test 2 transactions writing to the same key in multiple orders and
// with/without snapshots
Transaction* txn1 = txn_db->BeginTransaction(write_options);
Transaction* txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->Put("1", "1"));
ASSERT_OK(txn2->Put("1", "2"));
ASSERT_OK(txn1->Commit());
Status s = txn2->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
delete txn2;
txn_options.set_snapshot = true;
txn1 = txn_db->BeginTransaction(write_options, txn_options);
read_options1.snapshot = txn1->GetSnapshot();
txn2 = txn_db->BeginTransaction(write_options, txn_options);
read_options2.snapshot = txn2->GetSnapshot();
ASSERT_OK(txn1->Put("1", "3"));
ASSERT_OK(txn2->Put("1", "4"));
ASSERT_OK(txn1->Commit());
s = txn2->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
delete txn2;
txn1 = txn_db->BeginTransaction(write_options, txn_options);
read_options1.snapshot = txn1->GetSnapshot();
txn2 = txn_db->BeginTransaction(write_options, txn_options);
read_options2.snapshot = txn2->GetSnapshot();
ASSERT_OK(txn1->Put("1", "5"));
ASSERT_OK(txn1->Commit());
ASSERT_OK(txn2->Put("1", "6"));
s = txn2->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
delete txn2;
txn1 = txn_db->BeginTransaction(write_options, txn_options);
read_options1.snapshot = txn1->GetSnapshot();
txn2 = txn_db->BeginTransaction(write_options, txn_options);
read_options2.snapshot = txn2->GetSnapshot();
ASSERT_OK(txn1->Put("1", "5"));
ASSERT_OK(txn1->Commit());
txn2->SetSnapshot();
ASSERT_OK(txn2->Put("1", "6"));
ASSERT_OK(txn2->Commit());
delete txn1;
delete txn2;
txn1 = txn_db->BeginTransaction(write_options);
txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->Put("1", "7"));
ASSERT_OK(txn1->Commit());
ASSERT_OK(txn2->Put("1", "8"));
ASSERT_OK(txn2->Commit());
delete txn1;
delete txn2;
ASSERT_OK(txn_db->Get(read_options, "1", &value));
ASSERT_EQ(value, "8");
}
TEST_P(OptimisticTransactionTest, UntrackedWrites) {
WriteOptions write_options;
ReadOptions read_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
Status s;
// Verify transaction rollback works for untracked keys.
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn->PutUntracked("untracked", "0"));
ASSERT_OK(txn->Rollback());
s = txn_db->Get(read_options, "untracked", &value);
ASSERT_TRUE(s.IsNotFound());
delete txn;
txn = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn->Put("tracked", "1"));
ASSERT_OK(txn->PutUntracked("untracked", "1"));
ASSERT_OK(txn->MergeUntracked("untracked", "2"));
ASSERT_OK(txn->DeleteUntracked("untracked"));
// Write to the untracked key outside of the transaction and verify
// it doesn't prevent the transaction from committing.
ASSERT_OK(txn_db->Put(write_options, "untracked", "x"));
ASSERT_OK(txn->Commit());
s = txn_db->Get(read_options, "untracked", &value);
ASSERT_TRUE(s.IsNotFound());
delete txn;
txn = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn->Put("tracked", "10"));
ASSERT_OK(txn->PutUntracked("untracked", "A"));
// Write to tracked key outside of the transaction and verify that the
// untracked keys are not written when the commit fails.
ASSERT_OK(txn_db->Delete(write_options, "tracked"));
s = txn->Commit();
ASSERT_TRUE(s.IsBusy());
s = txn_db->Get(read_options, "untracked", &value);
ASSERT_TRUE(s.IsNotFound());
delete txn;
}
TEST_P(OptimisticTransactionTest, IteratorTest) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
// Write some keys to the db
ASSERT_OK(txn_db->Put(write_options, "A", "a"));
ASSERT_OK(txn_db->Put(write_options, "G", "g"));
ASSERT_OK(txn_db->Put(write_options, "F", "f"));
ASSERT_OK(txn_db->Put(write_options, "C", "c"));
ASSERT_OK(txn_db->Put(write_options, "D", "d"));
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
// Write some keys in a txn
ASSERT_OK(txn->Put("B", "b"));
ASSERT_OK(txn->Put("H", "h"));
ASSERT_OK(txn->Delete("D"));
ASSERT_OK(txn->Put("E", "e"));
txn->SetSnapshot();
const Snapshot* snapshot = txn->GetSnapshot();
// Write some keys to the db after the snapshot
ASSERT_OK(txn_db->Put(write_options, "BB", "xx"));
ASSERT_OK(txn_db->Put(write_options, "C", "xx"));
read_options.snapshot = snapshot;
Iterator* iter = txn->GetIterator(read_options);
ASSERT_OK(iter->status());
iter->SeekToFirst();
// Read all keys via iter and lock them all
std::string results[] = {"a", "b", "c", "e", "f", "g", "h"};
for (int i = 0; i < 7; i++) {
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ(results[i], iter->value().ToString());
ASSERT_OK(txn->GetForUpdate(read_options, iter->key(), nullptr));
iter->Next();
}
ASSERT_FALSE(iter->Valid());
iter->Seek("G");
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ("g", iter->value().ToString());
iter->Prev();
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ("f", iter->value().ToString());
iter->Seek("D");
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ("e", iter->value().ToString());
iter->Seek("C");
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ("c", iter->value().ToString());
iter->Next();
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ("e", iter->value().ToString());
iter->Seek("");
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ("a", iter->value().ToString());
iter->Seek("X");
ASSERT_OK(iter->status());
ASSERT_FALSE(iter->Valid());
iter->SeekToLast();
ASSERT_OK(iter->status());
ASSERT_TRUE(iter->Valid());
ASSERT_EQ("h", iter->value().ToString());
// key "C" was modified in the db after txn's snapshot. txn will not commit.
Status s = txn->Commit();
ASSERT_TRUE(s.IsBusy());
delete iter;
delete txn;
}
TEST_P(OptimisticTransactionTest, DeleteRangeSupportTest) {
// `OptimisticTransactionDB` does not allow range deletion in any API.
ASSERT_TRUE(
txn_db
->DeleteRange(WriteOptions(), txn_db->DefaultColumnFamily(), "a", "b")
.IsNotSupported());
WriteBatch wb;
ASSERT_OK(wb.DeleteRange("a", "b"));
ASSERT_NOK(txn_db->Write(WriteOptions(), &wb));
}
TEST_P(OptimisticTransactionTest, SavepointTest) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
Transaction* txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
Status s = txn->RollbackToSavePoint();
ASSERT_TRUE(s.IsNotFound());
txn->SetSavePoint(); // 1
ASSERT_OK(txn->RollbackToSavePoint()); // Rollback to beginning of txn
s = txn->RollbackToSavePoint();
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn->Put("B", "b"));
ASSERT_OK(txn->Commit());
ASSERT_OK(txn_db->Get(read_options, "B", &value));
ASSERT_EQ("b", value);
delete txn;
txn = txn_db->BeginTransaction(write_options);
ASSERT_NE(txn, nullptr);
ASSERT_OK(txn->Put("A", "a"));
ASSERT_OK(txn->Put("B", "bb"));
ASSERT_OK(txn->Put("C", "c"));
txn->SetSavePoint(); // 2
ASSERT_OK(txn->Delete("B"));
ASSERT_OK(txn->Put("C", "cc"));
ASSERT_OK(txn->Put("D", "d"));
ASSERT_OK(txn->RollbackToSavePoint()); // Rollback to 2
ASSERT_OK(txn->Get(read_options, "A", &value));
ASSERT_EQ("a", value);
ASSERT_OK(txn->Get(read_options, "B", &value));
ASSERT_EQ("bb", value);
ASSERT_OK(txn->Get(read_options, "C", &value));
ASSERT_EQ("c", value);
s = txn->Get(read_options, "D", &value);
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn->Put("A", "a"));
ASSERT_OK(txn->Put("E", "e"));
// Rollback to beginning of txn
s = txn->RollbackToSavePoint();
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn->Rollback());
s = txn->Get(read_options, "A", &value);
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn->Get(read_options, "B", &value));
ASSERT_EQ("b", value);
s = txn->Get(read_options, "D", &value);
ASSERT_TRUE(s.IsNotFound());
s = txn->Get(read_options, "D", &value);
ASSERT_TRUE(s.IsNotFound());
s = txn->Get(read_options, "E", &value);
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn->Put("A", "aa"));
ASSERT_OK(txn->Put("F", "f"));
txn->SetSavePoint(); // 3
txn->SetSavePoint(); // 4
ASSERT_OK(txn->Put("G", "g"));
ASSERT_OK(txn->Delete("F"));
ASSERT_OK(txn->Delete("B"));
ASSERT_OK(txn->Get(read_options, "A", &value));
ASSERT_EQ("aa", value);
s = txn->Get(read_options, "F", &value);
ASSERT_TRUE(s.IsNotFound());
s = txn->Get(read_options, "B", &value);
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn->RollbackToSavePoint()); // Rollback to 3
ASSERT_OK(txn->Get(read_options, "F", &value));
ASSERT_EQ("f", value);
s = txn->Get(read_options, "G", &value);
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn->Commit());
ASSERT_OK(txn_db->Get(read_options, "F", &value));
ASSERT_EQ("f", value);
s = txn_db->Get(read_options, "G", &value);
ASSERT_TRUE(s.IsNotFound());
ASSERT_OK(txn_db->Get(read_options, "A", &value));
ASSERT_EQ("aa", value);
ASSERT_OK(txn_db->Get(read_options, "B", &value));
ASSERT_EQ("b", value);
s = txn_db->Get(read_options, "C", &value);
ASSERT_TRUE(s.IsNotFound());
s = txn_db->Get(read_options, "D", &value);
ASSERT_TRUE(s.IsNotFound());
s = txn_db->Get(read_options, "E", &value);
ASSERT_TRUE(s.IsNotFound());
delete txn;
}
TEST_P(OptimisticTransactionTest, UndoGetForUpdateTest) {
WriteOptions write_options;
ReadOptions read_options, snapshot_read_options;
OptimisticTransactionOptions txn_options;
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
std::string value;
ASSERT_OK(txn_db->Put(write_options, "A", ""));
Transaction* txn1 = txn_db->BeginTransaction(write_options);
ASSERT_TRUE(txn1);
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->UndoGetForUpdate("A");
Transaction* txn2 = txn_db->BeginTransaction(write_options);
txn2->Put("A", "x");
ASSERT_OK(txn2->Commit());
delete txn2;
// Verify that txn1 can commit since A isn't conflict checked
ASSERT_OK(txn1->Commit());
delete txn1;
txn1 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->Put("A", "a"));
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->UndoGetForUpdate("A");
txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn2->Put("A", "x"));
ASSERT_OK(txn2->Commit());
delete txn2;
// Verify that txn1 cannot commit since A will still be conflict checked
Status s = txn1->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
txn1 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->UndoGetForUpdate("A");
txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn2->Put("A", "x"));
ASSERT_OK(txn2->Commit());
delete txn2;
// Verify that txn1 cannot commit since A will still be conflict checked
s = txn1->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
txn1 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->UndoGetForUpdate("A");
txn1->UndoGetForUpdate("A");
txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn2->Put("A", "x"));
ASSERT_OK(txn2->Commit());
delete txn2;
// Verify that txn1 can commit since A isn't conflict checked
ASSERT_OK(txn1->Commit());
delete txn1;
txn1 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->SetSavePoint();
txn1->UndoGetForUpdate("A");
txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn2->Put("A", "x"));
ASSERT_OK(txn2->Commit());
delete txn2;
// Verify that txn1 cannot commit since A will still be conflict checked
s = txn1->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
txn1 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->SetSavePoint();
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->UndoGetForUpdate("A");
txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn2->Put("A", "x"));
ASSERT_OK(txn2->Commit());
delete txn2;
// Verify that txn1 cannot commit since A will still be conflict checked
s = txn1->Commit();
ASSERT_TRUE(s.IsBusy());
delete txn1;
txn1 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->SetSavePoint();
ASSERT_OK(txn1->GetForUpdate(read_options, "A", &value));
txn1->UndoGetForUpdate("A");
ASSERT_OK(txn1->RollbackToSavePoint());
txn1->UndoGetForUpdate("A");
txn2 = txn_db->BeginTransaction(write_options);
ASSERT_OK(txn2->Put("A", "x"));
ASSERT_OK(txn2->Commit());
delete txn2;
// Verify that txn1 can commit since A isn't conflict checked
ASSERT_OK(txn1->Commit());
delete txn1;
}
namespace {
Status OptimisticTransactionStressTestInserter(OptimisticTransactionDB* db,
const size_t num_transactions,
const size_t num_sets,
const size_t num_keys_per_set) {
size_t seed = std::hash<std::thread::id>()(std::this_thread::get_id());
Random64 _rand(seed);
WriteOptions write_options;
ReadOptions read_options;
OptimisticTransactionOptions txn_options;
txn_options.set_snapshot = true;
RandomTransactionInserter inserter(&_rand, write_options, read_options,
num_keys_per_set,
static_cast<uint16_t>(num_sets));
for (size_t t = 0; t < num_transactions; t++) {
bool success = inserter.OptimisticTransactionDBInsert(db, txn_options);
if (!success) {
// unexpected failure
return inserter.GetLastStatus();
}
}
inserter.GetLastStatus().PermitUncheckedError();
// Make sure at least some of the transactions succeeded. It's ok if
// some failed due to write-conflicts.
if (inserter.GetFailureCount() > num_transactions / 2) {
return Status::TryAgain("Too many transactions failed! " +
std::to_string(inserter.GetFailureCount()) + " / " +
std::to_string(num_transactions));
}
return Status::OK();
}
} // namespace
TEST_P(OptimisticTransactionTest, OptimisticTransactionStressTest) {
const size_t num_threads = 4;
const size_t num_transactions_per_thread = 10000;
const size_t num_sets = 3;
const size_t num_keys_per_set = 100;
// Setting the key-space to be 100 keys should cause enough write-conflicts
// to make this test interesting.
std::vector<port::Thread> threads;
std::function<void()> call_inserter = [&] {
ASSERT_OK(OptimisticTransactionStressTestInserter(
txn_db, num_transactions_per_thread, num_sets, num_keys_per_set));
};
// Create N threads that use RandomTransactionInserter to write
// many transactions.
for (uint32_t i = 0; i < num_threads; i++) {
threads.emplace_back(call_inserter);
}
// Wait for all threads to run
for (auto& t : threads) {
t.join();
}
// Verify that data is consistent
Status s = RandomTransactionInserter::Verify(txn_db, num_sets);
ASSERT_OK(s);
}
TEST_P(OptimisticTransactionTest, SequenceNumberAfterRecoverTest) {
WriteOptions write_options;
OptimisticTransactionOptions transaction_options;
Transaction* transaction(txn_db->BeginTransaction(write_options, transaction_options));
Status s = transaction->Put("foo", "val");
ASSERT_OK(s);
s = transaction->Put("foo2", "val");
ASSERT_OK(s);
s = transaction->Put("foo3", "val");
ASSERT_OK(s);
s = transaction->Commit();
ASSERT_OK(s);
delete transaction;
Reopen();
transaction = txn_db->BeginTransaction(write_options, transaction_options);
s = transaction->Put("bar", "val");
ASSERT_OK(s);
s = transaction->Put("bar2", "val");
ASSERT_OK(s);
s = transaction->Commit();
ASSERT_OK(s);
delete transaction;
}
Snapshots with user-specified timestamps (#9879) Summary: In RocksDB, keys are associated with (internal) sequence numbers which denote when the keys are written to the database. Sequence numbers in different RocksDB instances are unrelated, thus not comparable. It is nice if we can associate sequence numbers with their corresponding actual timestamps. One thing we can do is to support user-defined timestamp, which allows the applications to specify the format of custom timestamps and encode a timestamp with each key. More details can be found at https://github.com/facebook/rocksdb/wiki/User-defined-Timestamp-%28Experimental%29. This PR provides a different but complementary approach. We can associate rocksdb snapshots (defined in https://github.com/facebook/rocksdb/blob/7.2.fb/include/rocksdb/snapshot.h#L20) with **user-specified** timestamps. Since a snapshot is essentially an object representing a sequence number, this PR establishes a bi-directional mapping between sequence numbers and timestamps. In the past, snapshots are usually taken by readers. The current super-version is grabbed, and a `rocksdb::Snapshot` object is created with the last published sequence number of the super-version. You can see that the reader actually has no good idea of what timestamp to assign to this snapshot, because by the time the `GetSnapshot()` is called, an arbitrarily long period of time may have already elapsed since the last write, which is when the last published sequence number is written. This observation motivates the creation of "timestamped" snapshots on the write path. Currently, this functionality is exposed only to the layer of `TransactionDB`. Application can tell RocksDB to create a snapshot when a transaction commits, effectively associating the last sequence number with a timestamp. It is also assumed that application will ensure any two snapshots with timestamps should satisfy the following: ``` snapshot1.seq < snapshot2.seq iff. snapshot1.ts < snapshot2.ts ``` If the application can guarantee that when a reader takes a timestamped snapshot, there is no active writes going on in the database, then we also allow the user to use a new API `TransactionDB::CreateTimestampedSnapshot()` to create a snapshot with associated timestamp. Code example ```cpp // Create a timestamped snapshot when committing transaction. txn->SetCommitTimestamp(100); txn->SetSnapshotOnNextOperation(); txn->Commit(); // A wrapper API for convenience Status Transaction::CommitAndTryCreateSnapshot( std::shared_ptr<TransactionNotifier> notifier, TxnTimestamp ts, std::shared_ptr<const Snapshot>* ret); // Create a timestamped snapshot if caller guarantees no concurrent writes std::pair<Status, std::shared_ptr<const Snapshot>> snapshot = txn_db->CreateTimestampedSnapshot(100); ``` The snapshots created in this way will be managed by RocksDB with ref-counting and potentially shared with other readers. We provide the following APIs for readers to retrieve a snapshot given a timestamp. ```cpp // Return the timestamped snapshot correponding to given timestamp. If ts is // kMaxTxnTimestamp, then we return the latest timestamped snapshot if present. // Othersise, we return the snapshot whose timestamp is equal to `ts`. If no // such snapshot exists, then we return null. std::shared_ptr<const Snapshot> TransactionDB::GetTimestampedSnapshot(TxnTimestamp ts) const; // Return the latest timestamped snapshot if present. std::shared_ptr<const Snapshot> TransactionDB::GetLatestTimestampedSnapshot() const; ``` We also provide two additional APIs for stats collection and reporting purposes. ```cpp Status TransactionDB::GetAllTimestampedSnapshots( std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; // Return timestamped snapshots whose timestamps fall in [ts_lb, ts_ub) and store them in `snapshots`. Status TransactionDB::GetTimestampedSnapshots( TxnTimestamp ts_lb, TxnTimestamp ts_ub, std::vector<std::shared_ptr<const Snapshot>>& snapshots) const; ``` To prevent the number of timestamped snapshots from growing infinitely, we provide the following API to release timestamped snapshots whose timestamps are older than or equal to a given threshold. ```cpp void TransactionDB::ReleaseTimestampedSnapshotsOlderThan(TxnTimestamp ts); ``` Before shutdown, RocksDB will release all timestamped snapshots. Comparison with user-defined timestamp and how they can be combined: User-defined timestamp persists every key with a timestamp, while timestamped snapshots maintain a volatile mapping between snapshots (sequence numbers) and timestamps. Different internal keys with the same user key but different timestamps will be treated as different by compaction, thus a newer version will not hide older versions (with smaller timestamps) unless they are eligible for garbage collection. In contrast, taking a timestamped snapshot at a certain sequence number and timestamp prevents all the keys visible in this snapshot from been dropped by compaction. Here, visible means (seq < snapshot and most recent). The timestamped snapshot supports the semantics of reading at an exact point in time. Timestamped snapshots can also be used with user-defined timestamp. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9879 Test Plan: ``` make check TEST_TMPDIR=/dev/shm make crash_test_with_txn ``` Reviewed By: siying Differential Revision: D35783919 Pulled By: riversand963 fbshipit-source-id: 586ad905e169189e19d3bfc0cb0177a7239d1bd4
2 years ago
TEST_P(OptimisticTransactionTest, TimestampedSnapshotMissingCommitTs) {
std::unique_ptr<Transaction> txn(txn_db->BeginTransaction(WriteOptions()));
ASSERT_OK(txn->Put("a", "v"));
Status s = txn->CommitAndTryCreateSnapshot();
ASSERT_TRUE(s.IsInvalidArgument());
}
TEST_P(OptimisticTransactionTest, TimestampedSnapshotSetCommitTs) {
std::unique_ptr<Transaction> txn(txn_db->BeginTransaction(WriteOptions()));
ASSERT_OK(txn->Put("a", "v"));
std::shared_ptr<const Snapshot> snapshot;
Status s = txn->CommitAndTryCreateSnapshot(nullptr, /*ts=*/100, &snapshot);
ASSERT_TRUE(s.IsNotSupported());
}
INSTANTIATE_TEST_CASE_P(
InstanceOccGroup, OptimisticTransactionTest,
testing::Values(OccValidationPolicy::kValidateSerial,
OccValidationPolicy::kValidateParallel));
} // namespace ROCKSDB_NAMESPACE
int main(int argc, char** argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
#else
#include <stdio.h>
int main(int /*argc*/, char** /*argv*/) {
fprintf(
stderr,
"SKIPPED as optimistic_transaction is not supported in ROCKSDB_LITE\n");
return 0;
}
#endif // !ROCKSDB_LITE