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rocksdb/utilities/transactions/write_prepared_txn_db.cc

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// 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
#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif
#include "utilities/transactions/write_prepared_txn_db.h"
#include <inttypes.h>
#include <algorithm>
#include <string>
#include <unordered_set>
#include <vector>
#include "db/db_impl.h"
#include "rocksdb/db.h"
#include "rocksdb/options.h"
#include "rocksdb/utilities/transaction_db.h"
#include "util/cast_util.h"
#include "util/mutexlock.h"
#include "util/string_util.h"
#include "util/sync_point.h"
#include "utilities/transactions/pessimistic_transaction.h"
#include "utilities/transactions/transaction_db_mutex_impl.h"
namespace rocksdb {
Status WritePreparedTxnDB::Initialize(
const std::vector<size_t>& compaction_enabled_cf_indices,
const std::vector<ColumnFamilyHandle*>& handles) {
auto dbimpl = reinterpret_cast<DBImpl*>(GetRootDB());
assert(dbimpl != nullptr);
auto rtxns = dbimpl->recovered_transactions();
for (auto rtxn : rtxns) {
// There should only one batch for WritePrepared policy.
assert(rtxn.second->batches_.size() == 1);
const auto& seq = rtxn.second->batches_.begin()->first;
const auto& batch_info = rtxn.second->batches_.begin()->second;
auto cnt = batch_info.batch_cnt_ ? batch_info.batch_cnt_ : 1;
for (size_t i = 0; i < cnt; i++) {
AddPrepared(seq + i);
}
}
SequenceNumber prev_max = max_evicted_seq_;
SequenceNumber last_seq = db_impl_->GetLatestSequenceNumber();
AdvanceMaxEvictedSeq(prev_max, last_seq);
// Create a gap between max and the next snapshot. This simplifies the logic
// in IsInSnapshot by not having to consider the special case of max ==
// snapshot after recovery. This is tested in IsInSnapshotEmptyMapTest.
if (last_seq) {
db_impl_->versions_->SetLastAllocatedSequence(last_seq + 1);
db_impl_->versions_->SetLastSequence(last_seq + 1);
db_impl_->versions_->SetLastPublishedSequence(last_seq + 1);
}
db_impl_->SetSnapshotChecker(new WritePreparedSnapshotChecker(this));
// A callback to commit a single sub-batch
class CommitSubBatchPreReleaseCallback : public PreReleaseCallback {
public:
explicit CommitSubBatchPreReleaseCallback(WritePreparedTxnDB* db)
: db_(db) {}
Status Callback(SequenceNumber commit_seq,
bool is_mem_disabled __attribute__((__unused__)),
uint64_t) override {
assert(!is_mem_disabled);
db_->AddCommitted(commit_seq, commit_seq);
return Status::OK();
}
private:
WritePreparedTxnDB* db_;
};
db_impl_->SetRecoverableStatePreReleaseCallback(
new CommitSubBatchPreReleaseCallback(this));
auto s = PessimisticTransactionDB::Initialize(compaction_enabled_cf_indices,
handles);
return s;
}
Status WritePreparedTxnDB::VerifyCFOptions(
const ColumnFamilyOptions& cf_options) {
Status s = PessimisticTransactionDB::VerifyCFOptions(cf_options);
if (!s.ok()) {
return s;
}
if (!cf_options.memtable_factory->CanHandleDuplicatedKey()) {
return Status::InvalidArgument(
"memtable_factory->CanHandleDuplicatedKey() cannot be false with "
"WritePrpeared transactions");
}
return Status::OK();
}
Transaction* WritePreparedTxnDB::BeginTransaction(
const WriteOptions& write_options, const TransactionOptions& txn_options,
Transaction* old_txn) {
if (old_txn != nullptr) {
ReinitializeTransaction(old_txn, write_options, txn_options);
return old_txn;
} else {
return new WritePreparedTxn(this, write_options, txn_options);
}
}
Status WritePreparedTxnDB::Write(const WriteOptions& opts,
WriteBatch* updates) {
if (txn_db_options_.skip_concurrency_control) {
// Skip locking the rows
const size_t UNKNOWN_BATCH_CNT = 0;
WritePreparedTxn* NO_TXN = nullptr;
return WriteInternal(opts, updates, UNKNOWN_BATCH_CNT, NO_TXN);
} else {
return PessimisticTransactionDB::WriteWithConcurrencyControl(opts, updates);
}
}
Status WritePreparedTxnDB::Write(
const WriteOptions& opts,
const TransactionDBWriteOptimizations& optimizations, WriteBatch* updates) {
if (optimizations.skip_concurrency_control) {
// Skip locking the rows
const size_t UNKNOWN_BATCH_CNT = 0;
const size_t ONE_BATCH_CNT = 1;
const size_t batch_cnt = optimizations.skip_duplicate_key_check
? ONE_BATCH_CNT
: UNKNOWN_BATCH_CNT;
WritePreparedTxn* NO_TXN = nullptr;
return WriteInternal(opts, updates, batch_cnt, NO_TXN);
} else {
// TODO(myabandeh): Make use of skip_duplicate_key_check hint
// Fall back to unoptimized version
return PessimisticTransactionDB::WriteWithConcurrencyControl(opts, updates);
}
}
Status WritePreparedTxnDB::WriteInternal(const WriteOptions& write_options_orig,
WriteBatch* batch, size_t batch_cnt,
WritePreparedTxn* txn) {
ROCKS_LOG_DETAILS(db_impl_->immutable_db_options().info_log,
"CommitBatchInternal");
if (batch->Count() == 0) {
// Otherwise our 1 seq per batch logic will break since there is no seq
// increased for this batch.
return Status::OK();
}
if (batch_cnt == 0) { // not provided, then compute it
// TODO(myabandeh): add an option to allow user skipping this cost
SubBatchCounter counter(*GetCFComparatorMap());
auto s = batch->Iterate(&counter);
assert(s.ok());
batch_cnt = counter.BatchCount();
WPRecordTick(TXN_DUPLICATE_KEY_OVERHEAD);
ROCKS_LOG_DETAILS(info_log_, "Duplicate key overhead: %" PRIu64 " batches",
static_cast<uint64_t>(batch_cnt));
}
assert(batch_cnt);
bool do_one_write = !db_impl_->immutable_db_options().two_write_queues;
WriteOptions write_options(write_options_orig);
// In the absence of Prepare markers, use Noop as a batch separator
WriteBatchInternal::InsertNoop(batch);
const bool DISABLE_MEMTABLE = true;
const uint64_t no_log_ref = 0;
uint64_t seq_used = kMaxSequenceNumber;
const size_t ZERO_PREPARES = 0;
const bool kSeperatePrepareCommitBatches = true;
// Since this is not 2pc, there is no need for AddPrepared but having it in
// the PreReleaseCallback enables an optimization. Refer to
// SmallestUnCommittedSeq for more details.
AddPreparedCallback add_prepared_callback(
this, db_impl_, batch_cnt,
db_impl_->immutable_db_options().two_write_queues,
!kSeperatePrepareCommitBatches);
WritePreparedCommitEntryPreReleaseCallback update_commit_map(
this, db_impl_, kMaxSequenceNumber, ZERO_PREPARES, batch_cnt);
PreReleaseCallback* pre_release_callback;
if (do_one_write) {
pre_release_callback = &update_commit_map;
} else {
pre_release_callback = &add_prepared_callback;
}
auto s = db_impl_->WriteImpl(write_options, batch, nullptr, nullptr,
no_log_ref, !DISABLE_MEMTABLE, &seq_used,
batch_cnt, pre_release_callback);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
uint64_t prepare_seq = seq_used;
if (txn != nullptr) {
txn->SetId(prepare_seq);
}
if (!s.ok()) {
return s;
}
if (do_one_write) {
return s;
} // else do the 2nd write for commit
ROCKS_LOG_DETAILS(db_impl_->immutable_db_options().info_log,
"CommitBatchInternal 2nd write prepare_seq: %" PRIu64,
prepare_seq);
// Commit the batch by writing an empty batch to the 2nd queue that will
// release the commit sequence number to readers.
const size_t ZERO_COMMITS = 0;
WritePreparedCommitEntryPreReleaseCallback update_commit_map_with_prepare(
this, db_impl_, prepare_seq, batch_cnt, ZERO_COMMITS);
WriteBatch empty_batch;
write_options.disableWAL = true;
write_options.sync = false;
const size_t ONE_BATCH = 1; // Just to inc the seq
s = db_impl_->WriteImpl(write_options, &empty_batch, nullptr, nullptr,
no_log_ref, DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
&update_commit_map_with_prepare);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
// Note RemovePrepared should be called after WriteImpl that publishsed the
// seq. Otherwise SmallestUnCommittedSeq optimization breaks.
RemovePrepared(prepare_seq, batch_cnt);
return s;
}
Status WritePreparedTxnDB::Get(const ReadOptions& options,
ColumnFamilyHandle* column_family,
const Slice& key, PinnableSlice* value) {
SequenceNumber min_uncommitted, snap_seq;
const bool backed_by_snapshot =
AssignMinMaxSeqs(options.snapshot, &min_uncommitted, &snap_seq);
WritePreparedTxnReadCallback callback(this, snap_seq, min_uncommitted);
bool* dont_care = nullptr;
auto res = db_impl_->GetImpl(options, column_family, key, value, dont_care,
&callback);
if (LIKELY(
ValidateSnapshot(callback.max_visible_seq(), backed_by_snapshot))) {
return res;
} else {
return Status::TryAgain();
}
}
void WritePreparedTxnDB::UpdateCFComparatorMap(
const std::vector<ColumnFamilyHandle*>& handles) {
auto cf_map = new std::map<uint32_t, const Comparator*>();
auto handle_map = new std::map<uint32_t, ColumnFamilyHandle*>();
for (auto h : handles) {
auto id = h->GetID();
const Comparator* comparator = h->GetComparator();
(*cf_map)[id] = comparator;
if (id != 0) {
(*handle_map)[id] = h;
} else {
// The pointer to the default cf handle in the handles will be deleted.
// Use the pointer maintained by the db instead.
(*handle_map)[id] = DefaultColumnFamily();
}
}
cf_map_.reset(cf_map);
handle_map_.reset(handle_map);
}
void WritePreparedTxnDB::UpdateCFComparatorMap(ColumnFamilyHandle* h) {
auto old_cf_map_ptr = cf_map_.get();
assert(old_cf_map_ptr);
auto cf_map = new std::map<uint32_t, const Comparator*>(*old_cf_map_ptr);
auto old_handle_map_ptr = handle_map_.get();
assert(old_handle_map_ptr);
auto handle_map =
new std::map<uint32_t, ColumnFamilyHandle*>(*old_handle_map_ptr);
auto id = h->GetID();
const Comparator* comparator = h->GetComparator();
(*cf_map)[id] = comparator;
(*handle_map)[id] = h;
cf_map_.reset(cf_map);
handle_map_.reset(handle_map);
}
std::vector<Status> WritePreparedTxnDB::MultiGet(
const ReadOptions& options,
const std::vector<ColumnFamilyHandle*>& column_family,
const std::vector<Slice>& keys, std::vector<std::string>* values) {
assert(values);
size_t num_keys = keys.size();
values->resize(num_keys);
std::vector<Status> stat_list(num_keys);
for (size_t i = 0; i < num_keys; ++i) {
std::string* value = values ? &(*values)[i] : nullptr;
stat_list[i] = this->Get(options, column_family[i], keys[i], value);
}
return stat_list;
}
// Struct to hold ownership of snapshot and read callback for iterator cleanup.
struct WritePreparedTxnDB::IteratorState {
IteratorState(WritePreparedTxnDB* txn_db, SequenceNumber sequence,
std::shared_ptr<ManagedSnapshot> s,
SequenceNumber min_uncommitted)
: callback(txn_db, sequence, min_uncommitted), snapshot(s) {}
WritePreparedTxnReadCallback callback;
std::shared_ptr<ManagedSnapshot> snapshot;
};
namespace {
static void CleanupWritePreparedTxnDBIterator(void* arg1, void* /*arg2*/) {
delete reinterpret_cast<WritePreparedTxnDB::IteratorState*>(arg1);
}
} // anonymous namespace
Iterator* WritePreparedTxnDB::NewIterator(const ReadOptions& options,
ColumnFamilyHandle* column_family) {
constexpr bool ALLOW_BLOB = true;
constexpr bool ALLOW_REFRESH = true;
std::shared_ptr<ManagedSnapshot> own_snapshot = nullptr;
SequenceNumber snapshot_seq = kMaxSequenceNumber;
SequenceNumber min_uncommitted = 0;
if (options.snapshot != nullptr) {
snapshot_seq = options.snapshot->GetSequenceNumber();
min_uncommitted =
static_cast_with_check<const SnapshotImpl, const Snapshot>(
options.snapshot)
->min_uncommitted_;
} else {
auto* snapshot = GetSnapshot();
// We take a snapshot to make sure that the related data in the commit map
// are not deleted.
snapshot_seq = snapshot->GetSequenceNumber();
min_uncommitted =
static_cast_with_check<const SnapshotImpl, const Snapshot>(snapshot)
->min_uncommitted_;
own_snapshot = std::make_shared<ManagedSnapshot>(db_impl_, snapshot);
}
assert(snapshot_seq != kMaxSequenceNumber);
auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
auto* state =
new IteratorState(this, snapshot_seq, own_snapshot, min_uncommitted);
auto* db_iter =
db_impl_->NewIteratorImpl(options, cfd, snapshot_seq, &state->callback,
!ALLOW_BLOB, !ALLOW_REFRESH);
db_iter->RegisterCleanup(CleanupWritePreparedTxnDBIterator, state, nullptr);
return db_iter;
}
Status WritePreparedTxnDB::NewIterators(
const ReadOptions& options,
const std::vector<ColumnFamilyHandle*>& column_families,
std::vector<Iterator*>* iterators) {
constexpr bool ALLOW_BLOB = true;
constexpr bool ALLOW_REFRESH = true;
std::shared_ptr<ManagedSnapshot> own_snapshot = nullptr;
SequenceNumber snapshot_seq = kMaxSequenceNumber;
SequenceNumber min_uncommitted = 0;
if (options.snapshot != nullptr) {
snapshot_seq = options.snapshot->GetSequenceNumber();
min_uncommitted = static_cast_with_check<const SnapshotImpl, const Snapshot>(
options.snapshot)
->min_uncommitted_;
} else {
auto* snapshot = GetSnapshot();
// We take a snapshot to make sure that the related data in the commit map
// are not deleted.
snapshot_seq = snapshot->GetSequenceNumber();
own_snapshot = std::make_shared<ManagedSnapshot>(db_impl_, snapshot);
min_uncommitted =
static_cast_with_check<const SnapshotImpl, const Snapshot>(snapshot)
->min_uncommitted_;
}
iterators->clear();
iterators->reserve(column_families.size());
for (auto* column_family : column_families) {
auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
auto* state =
new IteratorState(this, snapshot_seq, own_snapshot, min_uncommitted);
auto* db_iter =
db_impl_->NewIteratorImpl(options, cfd, snapshot_seq, &state->callback,
!ALLOW_BLOB, !ALLOW_REFRESH);
db_iter->RegisterCleanup(CleanupWritePreparedTxnDBIterator, state, nullptr);
iterators->push_back(db_iter);
}
return Status::OK();
}
void WritePreparedTxnDB::Init(const TransactionDBOptions& /* unused */) {
// Adcance max_evicted_seq_ no more than 100 times before the cache wraps
// around.
INC_STEP_FOR_MAX_EVICTED =
std::max(COMMIT_CACHE_SIZE / 100, static_cast<size_t>(1));
snapshot_cache_ = std::unique_ptr<std::atomic<SequenceNumber>[]>(
new std::atomic<SequenceNumber>[SNAPSHOT_CACHE_SIZE] {});
commit_cache_ = std::unique_ptr<std::atomic<CommitEntry64b>[]>(
new std::atomic<CommitEntry64b>[COMMIT_CACHE_SIZE] {});
}
void WritePreparedTxnDB::CheckPreparedAgainstMax(SequenceNumber new_max) {
prepared_mutex_.AssertHeld();
// When max_evicted_seq_ advances, move older entries from prepared_txns_
// to delayed_prepared_. This guarantees that if a seq is lower than max,
// then it is not in prepared_txns_ and save an expensive, synchronized
// lookup from a shared set. delayed_prepared_ is expected to be empty in
// normal cases.
ROCKS_LOG_DETAILS(
info_log_,
"CheckPreparedAgainstMax prepared_txns_.empty() %d top: %" PRIu64,
prepared_txns_.empty(),
prepared_txns_.empty() ? 0 : prepared_txns_.top());
while (!prepared_txns_.empty() && prepared_txns_.top() <= new_max) {
auto to_be_popped = prepared_txns_.top();
delayed_prepared_.insert(to_be_popped);
ROCKS_LOG_WARN(info_log_,
"prepared_mutex_ overhead %" PRIu64 " (prep=%" PRIu64
" new_max=%" PRIu64,
static_cast<uint64_t>(delayed_prepared_.size()),
to_be_popped, new_max);
prepared_txns_.pop();
delayed_prepared_empty_.store(false, std::memory_order_release);
}
}
void WritePreparedTxnDB::AddPrepared(uint64_t seq) {
ROCKS_LOG_DETAILS(info_log_, "Txn %" PRIu64 " Preparing with max %" PRIu64,
seq, max_evicted_seq_.load());
TEST_SYNC_POINT("AddPrepared::begin:pause");
TEST_SYNC_POINT("AddPrepared::begin:resume");
WriteLock wl(&prepared_mutex_);
prepared_txns_.push(seq);
auto new_max = future_max_evicted_seq_.load();
if (UNLIKELY(seq <= new_max)) {
// This should not happen in normal case
ROCKS_LOG_ERROR(
info_log_,
"Added prepare_seq is not larger than max_evicted_seq_: %" PRIu64
" <= %" PRIu64,
seq, new_max);
CheckPreparedAgainstMax(new_max);
}
TEST_SYNC_POINT("AddPrepared::end");
}
void WritePreparedTxnDB::AddCommitted(uint64_t prepare_seq, uint64_t commit_seq,
uint8_t loop_cnt) {
ROCKS_LOG_DETAILS(info_log_, "Txn %" PRIu64 " Committing with %" PRIu64,
prepare_seq, commit_seq);
TEST_SYNC_POINT("WritePreparedTxnDB::AddCommitted:start");
TEST_SYNC_POINT("WritePreparedTxnDB::AddCommitted:start:pause");
auto indexed_seq = prepare_seq % COMMIT_CACHE_SIZE;
CommitEntry64b evicted_64b;
CommitEntry evicted;
bool to_be_evicted = GetCommitEntry(indexed_seq, &evicted_64b, &evicted);
if (LIKELY(to_be_evicted)) {
assert(evicted.prep_seq != prepare_seq);
auto prev_max = max_evicted_seq_.load(std::memory_order_acquire);
ROCKS_LOG_DETAILS(info_log_,
"Evicting %" PRIu64 ",%" PRIu64 " with max %" PRIu64,
evicted.prep_seq, evicted.commit_seq, prev_max);
if (prev_max < evicted.commit_seq) {
auto last = db_impl_->GetLastPublishedSequence(); // could be 0
SequenceNumber max_evicted_seq;
if (LIKELY(evicted.commit_seq < last)) {
assert(last > 0);
// Inc max in larger steps to avoid frequent updates
max_evicted_seq =
std::min(evicted.commit_seq + INC_STEP_FOR_MAX_EVICTED, last - 1);
} else {
// legit when a commit entry in a write batch overwrite the previous one
max_evicted_seq = evicted.commit_seq;
}
ROCKS_LOG_DETAILS(info_log_,
"%lu Evicting %" PRIu64 ",%" PRIu64 " with max %" PRIu64
" => %lu",
prepare_seq, evicted.prep_seq, evicted.commit_seq,
prev_max, max_evicted_seq);
AdvanceMaxEvictedSeq(prev_max, max_evicted_seq);
}
// After each eviction from commit cache, check if the commit entry should
// be kept around because it overlaps with a live snapshot.
CheckAgainstSnapshots(evicted);
if (UNLIKELY(!delayed_prepared_empty_.load(std::memory_order_acquire))) {
WriteLock wl(&prepared_mutex_);
for (auto dp : delayed_prepared_) {
if (dp == evicted.prep_seq) {
// This is a rare case that txn is committed but prepared_txns_ is not
// cleaned up yet. Refer to delayed_prepared_commits_ definition for
// why it should be kept updated.
delayed_prepared_commits_[evicted.prep_seq] = evicted.commit_seq;
ROCKS_LOG_DEBUG(info_log_,
"delayed_prepared_commits_[%" PRIu64 "]=%" PRIu64,
evicted.prep_seq, evicted.commit_seq);
break;
}
}
}
}
bool succ =
ExchangeCommitEntry(indexed_seq, evicted_64b, {prepare_seq, commit_seq});
if (UNLIKELY(!succ)) {
ROCKS_LOG_ERROR(info_log_,
"ExchangeCommitEntry failed on [%" PRIu64 "] %" PRIu64
",%" PRIu64 " retrying...",
indexed_seq, prepare_seq, commit_seq);
// A very rare event, in which the commit entry is updated before we do.
// Here we apply a very simple solution of retrying.
if (loop_cnt > 100) {
throw std::runtime_error("Infinite loop in AddCommitted!");
}
AddCommitted(prepare_seq, commit_seq, ++loop_cnt);
return;
}
TEST_SYNC_POINT("WritePreparedTxnDB::AddCommitted:end");
TEST_SYNC_POINT("WritePreparedTxnDB::AddCommitted:end:pause");
}
void WritePreparedTxnDB::RemovePrepared(const uint64_t prepare_seq,
const size_t batch_cnt) {
TEST_SYNC_POINT_CALLBACK(
"RemovePrepared:Start",
const_cast<void*>(reinterpret_cast<const void*>(&prepare_seq)));
TEST_SYNC_POINT("WritePreparedTxnDB::RemovePrepared:pause");
TEST_SYNC_POINT("WritePreparedTxnDB::RemovePrepared:resume");
ROCKS_LOG_DETAILS(info_log_,
"RemovePrepared %" PRIu64 " cnt: %" ROCKSDB_PRIszt,
prepare_seq, batch_cnt);
WriteLock wl(&prepared_mutex_);
for (size_t i = 0; i < batch_cnt; i++) {
prepared_txns_.erase(prepare_seq + i);
bool was_empty = delayed_prepared_.empty();
if (!was_empty) {
delayed_prepared_.erase(prepare_seq + i);
auto it = delayed_prepared_commits_.find(prepare_seq + i);
if (it != delayed_prepared_commits_.end()) {
ROCKS_LOG_DETAILS(info_log_, "delayed_prepared_commits_.erase %" PRIu64,
prepare_seq + i);
delayed_prepared_commits_.erase(it);
}
bool is_empty = delayed_prepared_.empty();
if (was_empty != is_empty) {
delayed_prepared_empty_.store(is_empty, std::memory_order_release);
}
}
}
}
bool WritePreparedTxnDB::GetCommitEntry(const uint64_t indexed_seq,
CommitEntry64b* entry_64b,
CommitEntry* entry) const {
*entry_64b = commit_cache_[static_cast<size_t>(indexed_seq)].load(std::memory_order_acquire);
bool valid = entry_64b->Parse(indexed_seq, entry, FORMAT);
return valid;
}
bool WritePreparedTxnDB::AddCommitEntry(const uint64_t indexed_seq,
const CommitEntry& new_entry,
CommitEntry* evicted_entry) {
CommitEntry64b new_entry_64b(new_entry, FORMAT);
CommitEntry64b evicted_entry_64b = commit_cache_[static_cast<size_t>(indexed_seq)].exchange(
new_entry_64b, std::memory_order_acq_rel);
bool valid = evicted_entry_64b.Parse(indexed_seq, evicted_entry, FORMAT);
return valid;
}
bool WritePreparedTxnDB::ExchangeCommitEntry(const uint64_t indexed_seq,
CommitEntry64b& expected_entry_64b,
const CommitEntry& new_entry) {
auto& atomic_entry = commit_cache_[static_cast<size_t>(indexed_seq)];
CommitEntry64b new_entry_64b(new_entry, FORMAT);
bool succ = atomic_entry.compare_exchange_strong(
expected_entry_64b, new_entry_64b, std::memory_order_acq_rel,
std::memory_order_acquire);
return succ;
}
void WritePreparedTxnDB::AdvanceMaxEvictedSeq(const SequenceNumber& prev_max,
const SequenceNumber& new_max) {
ROCKS_LOG_DETAILS(info_log_,
"AdvanceMaxEvictedSeq overhead %" PRIu64 " => %" PRIu64,
prev_max, new_max);
// Declare the intention before getting snapshot from the DB. This helps a
// concurrent GetSnapshot to wait to catch up with future_max_evicted_seq_ if
// it has not already. Otherwise the new snapshot is when we ask DB for
// snapshots smaller than future max.
auto updated_future_max = prev_max;
while (updated_future_max < new_max &&
!future_max_evicted_seq_.compare_exchange_weak(
updated_future_max, new_max, std::memory_order_acq_rel,
std::memory_order_relaxed)) {
};
{
WriteLock wl(&prepared_mutex_);
CheckPreparedAgainstMax(new_max);
}
// With each change to max_evicted_seq_ fetch the live snapshots behind it.
// We use max as the version of snapshots to identify how fresh are the
// snapshot list. This works because the snapshots are between 0 and
// max, so the larger the max, the more complete they are.
SequenceNumber new_snapshots_version = new_max;
std::vector<SequenceNumber> snapshots;
bool update_snapshots = false;
if (new_snapshots_version > snapshots_version_) {
// This is to avoid updating the snapshots_ if it already updated
// with a more recent vesion by a concrrent thread
update_snapshots = true;
// We only care about snapshots lower then max
snapshots = GetSnapshotListFromDB(new_max);
}
if (update_snapshots) {
UpdateSnapshots(snapshots, new_snapshots_version);
if (!snapshots.empty()) {
WriteLock wl(&old_commit_map_mutex_);
for (auto snap : snapshots) {
// This allows IsInSnapshot to tell apart the reads from in valid
// snapshots from the reads from committed values in valid snapshots.
old_commit_map_[snap];
}
old_commit_map_empty_.store(false, std::memory_order_release);
}
}
auto updated_prev_max = prev_max;
TEST_SYNC_POINT("AdvanceMaxEvictedSeq::update_max:pause");
TEST_SYNC_POINT("AdvanceMaxEvictedSeq::update_max:resume");
while (updated_prev_max < new_max &&
!max_evicted_seq_.compare_exchange_weak(updated_prev_max, new_max,
std::memory_order_acq_rel,
std::memory_order_relaxed)) {
};
}
const Snapshot* WritePreparedTxnDB::GetSnapshot() {
const bool kForWWConflictCheck = true;
return GetSnapshotInternal(!kForWWConflictCheck);
}
SnapshotImpl* WritePreparedTxnDB::GetSnapshotInternal(
bool for_ww_conflict_check) {
// Note: for this optimization setting the last sequence number and obtaining
// the smallest uncommitted seq should be done atomically. However to avoid
// the mutex overhead, we call SmallestUnCommittedSeq BEFORE taking the
// snapshot. Since we always updated the list of unprepared seq (via
// AddPrepared) AFTER the last sequence is updated, this guarantees that the
// smallest uncommitted seq that we pair with the snapshot is smaller or equal
// the value that would be obtained otherwise atomically. That is ok since
// this optimization works as long as min_uncommitted is less than or equal
// than the smallest uncommitted seq when the snapshot was taken.
auto min_uncommitted = WritePreparedTxnDB::SmallestUnCommittedSeq();
SnapshotImpl* snap_impl = db_impl_->GetSnapshotImpl(for_ww_conflict_check);
assert(snap_impl);
SequenceNumber snap_seq = snap_impl->GetSequenceNumber();
// Note: Check against future_max_evicted_seq_ (in contrast with
// max_evicted_seq_) in case there is a concurrent AdvanceMaxEvictedSeq.
if (UNLIKELY(snap_seq != 0 && snap_seq <= future_max_evicted_seq_)) {
// There is a very rare case in which the commit entry evicts another commit
// entry that is not published yet thus advancing max evicted seq beyond the
// last published seq. This case is not likely in real-world setup so we
// handle it with a few retries.
size_t retry = 0;
SequenceNumber max;
while ((max = future_max_evicted_seq_.load()) != 0 &&
snap_impl->GetSequenceNumber() <= max && retry < 100) {
ROCKS_LOG_WARN(info_log_,
"GetSnapshot snap: %" PRIu64 " max: %" PRIu64
" retry %" ROCKSDB_PRIszt,
snap_impl->GetSequenceNumber(), max, retry);
ReleaseSnapshot(snap_impl);
// Wait for last visible seq to catch up with max, and also go beyond it
// by one.
AdvanceSeqByOne();
snap_impl = db_impl_->GetSnapshotImpl(for_ww_conflict_check);
assert(snap_impl);
retry++;
}
assert(snap_impl->GetSequenceNumber() > max);
if (snap_impl->GetSequenceNumber() <= max) {
throw std::runtime_error(
"Snapshot seq " + ToString(snap_impl->GetSequenceNumber()) +
" after " + ToString(retry) +
" retries is still less than futre_max_evicted_seq_" + ToString(max));
}
}
EnhanceSnapshot(snap_impl, min_uncommitted);
ROCKS_LOG_DETAILS(
db_impl_->immutable_db_options().info_log,
"GetSnapshot %" PRIu64 " ww:%" PRIi32 " min_uncommitted: %" PRIu64,
snap_impl->GetSequenceNumber(), for_ww_conflict_check, min_uncommitted);
return snap_impl;
}
void WritePreparedTxnDB::AdvanceSeqByOne() {
// Inserting an empty value will i) let the max evicted entry to be
// published, i.e., max == last_published, increase the last published to
// be one beyond max, i.e., max < last_published.
WriteOptions woptions;
TransactionOptions txn_options;
Transaction* txn0 = BeginTransaction(woptions, txn_options, nullptr);
std::hash<std::thread::id> hasher;
char name[64];
snprintf(name, 64, "txn%" ROCKSDB_PRIszt, hasher(std::this_thread::get_id()));
assert(strlen(name) < 64 - 1);
Status s = txn0->SetName(name);
assert(s.ok());
if (s.ok()) {
// Without prepare it would simply skip the commit
s = txn0->Prepare();
}
assert(s.ok());
if (s.ok()) {
s = txn0->Commit();
}
assert(s.ok());
delete txn0;
}
const std::vector<SequenceNumber> WritePreparedTxnDB::GetSnapshotListFromDB(
SequenceNumber max) {
ROCKS_LOG_DETAILS(info_log_, "GetSnapshotListFromDB with max %" PRIu64, max);
InstrumentedMutexLock dblock(db_impl_->mutex());
db_impl_->mutex()->AssertHeld();
return db_impl_->snapshots().GetAll(nullptr, max);
}
void WritePreparedTxnDB::ReleaseSnapshotInternal(
const SequenceNumber snap_seq) {
// TODO(myabandeh): relax should enough since the synchronizatin is already
// done by snapshots_mutex_ under which this function is called.
if (snap_seq <= max_evicted_seq_.load(std::memory_order_acquire)) {
// Then this is a rare case that transaction did not finish before max
// advances. It is expected for a few read-only backup snapshots. For such
// snapshots we might have kept around a couple of entries in the
// old_commit_map_. Check and do garbage collection if that is the case.
bool need_gc = false;
{
WPRecordTick(TXN_OLD_COMMIT_MAP_MUTEX_OVERHEAD);
ROCKS_LOG_WARN(info_log_, "old_commit_map_mutex_ overhead for %" PRIu64,
snap_seq);
ReadLock rl(&old_commit_map_mutex_);
auto prep_set_entry = old_commit_map_.find(snap_seq);
need_gc = prep_set_entry != old_commit_map_.end();
}
if (need_gc) {
WPRecordTick(TXN_OLD_COMMIT_MAP_MUTEX_OVERHEAD);
ROCKS_LOG_WARN(info_log_, "old_commit_map_mutex_ overhead for %" PRIu64,
snap_seq);
WriteLock wl(&old_commit_map_mutex_);
old_commit_map_.erase(snap_seq);
old_commit_map_empty_.store(old_commit_map_.empty(),
std::memory_order_release);
}
}
}
void WritePreparedTxnDB::CleanupReleasedSnapshots(
const std::vector<SequenceNumber>& new_snapshots,
const std::vector<SequenceNumber>& old_snapshots) {
auto newi = new_snapshots.begin();
auto oldi = old_snapshots.begin();
for (; newi != new_snapshots.end() && oldi != old_snapshots.end();) {
assert(*newi >= *oldi); // cannot have new snapshots with lower seq
if (*newi == *oldi) { // still not released
auto value = *newi;
while (newi != new_snapshots.end() && *newi == value) {
newi++;
}
while (oldi != old_snapshots.end() && *oldi == value) {
oldi++;
}
} else {
assert(*newi > *oldi); // *oldi is released
ReleaseSnapshotInternal(*oldi);
oldi++;
}
}
// Everything remained in old_snapshots is released and must be cleaned up
for (; oldi != old_snapshots.end(); oldi++) {
ReleaseSnapshotInternal(*oldi);
}
}
void WritePreparedTxnDB::UpdateSnapshots(
const std::vector<SequenceNumber>& snapshots,
const SequenceNumber& version) {
ROCKS_LOG_DETAILS(info_log_, "UpdateSnapshots with version %" PRIu64,
version);
TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:start");
TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:start");
#ifndef NDEBUG
size_t sync_i = 0;
#endif
ROCKS_LOG_DETAILS(info_log_, "snapshots_mutex_ overhead");
WriteLock wl(&snapshots_mutex_);
snapshots_version_ = version;
// We update the list concurrently with the readers.
// Both new and old lists are sorted and the new list is subset of the
// previous list plus some new items. Thus if a snapshot repeats in
// both new and old lists, it will appear upper in the new list. So if
// we simply insert the new snapshots in order, if an overwritten item
// is still valid in the new list is either written to the same place in
// the array or it is written in a higher palce before it gets
// overwritten by another item. This guarantess a reader that reads the
// list bottom-up will eventaully see a snapshot that repeats in the
// update, either before it gets overwritten by the writer or
// afterwards.
size_t i = 0;
auto it = snapshots.begin();
for (; it != snapshots.end() && i < SNAPSHOT_CACHE_SIZE; ++it, ++i) {
snapshot_cache_[i].store(*it, std::memory_order_release);
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:", ++sync_i);
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:", sync_i);
}
#ifndef NDEBUG
// Release the remaining sync points since they are useless given that the
// reader would also use lock to access snapshots
for (++sync_i; sync_i <= 10; ++sync_i) {
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:", sync_i);
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:", sync_i);
}
#endif
snapshots_.clear();
for (; it != snapshots.end(); ++it) {
// Insert them to a vector that is less efficient to access
// concurrently
snapshots_.push_back(*it);
}
// Update the size at the end. Otherwise a parallel reader might read
// items that are not set yet.
snapshots_total_.store(snapshots.size(), std::memory_order_release);
// Note: this must be done after the snapshots data structures are updated
// with the new list of snapshots.
CleanupReleasedSnapshots(snapshots, snapshots_all_);
snapshots_all_ = snapshots;
TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:end");
TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:end");
}
void WritePreparedTxnDB::CheckAgainstSnapshots(const CommitEntry& evicted) {
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:start");
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:start");
#ifndef NDEBUG
size_t sync_i = 0;
#endif
// First check the snapshot cache that is efficient for concurrent access
auto cnt = snapshots_total_.load(std::memory_order_acquire);
// The list might get updated concurrently as we are reading from it. The
// reader should be able to read all the snapshots that are still valid
// after the update. Since the survived snapshots are written in a higher
// place before gets overwritten the reader that reads bottom-up will
// eventully see it.
const bool next_is_larger = true;
// We will set to true if the border line snapshot suggests that.
bool search_larger_list = false;
size_t ip1 = std::min(cnt, SNAPSHOT_CACHE_SIZE);
for (; 0 < ip1; ip1--) {
SequenceNumber snapshot_seq =
snapshot_cache_[ip1 - 1].load(std::memory_order_acquire);
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:",
++sync_i);
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:", sync_i);
if (ip1 == SNAPSHOT_CACHE_SIZE) { // border line snapshot
// snapshot_seq < commit_seq => larger_snapshot_seq <= commit_seq
// then later also continue the search to larger snapshots
search_larger_list = snapshot_seq < evicted.commit_seq;
}
if (!MaybeUpdateOldCommitMap(evicted.prep_seq, evicted.commit_seq,
snapshot_seq, !next_is_larger)) {
break;
}
}
#ifndef NDEBUG
// Release the remaining sync points before accquiring the lock
for (++sync_i; sync_i <= 10; ++sync_i) {
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:", sync_i);
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:", sync_i);
}
#endif
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:end");
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:end");
if (UNLIKELY(SNAPSHOT_CACHE_SIZE < cnt && search_larger_list)) {
// Then access the less efficient list of snapshots_
WPRecordTick(TXN_SNAPSHOT_MUTEX_OVERHEAD);
ROCKS_LOG_WARN(info_log_,
"snapshots_mutex_ overhead for <%" PRIu64 ",%" PRIu64
"> with %" ROCKSDB_PRIszt " snapshots",
evicted.prep_seq, evicted.commit_seq, cnt);
ReadLock rl(&snapshots_mutex_);
// Items could have moved from the snapshots_ to snapshot_cache_ before
// accquiring the lock. To make sure that we do not miss a valid snapshot,
// read snapshot_cache_ again while holding the lock.
for (size_t i = 0; i < SNAPSHOT_CACHE_SIZE; i++) {
SequenceNumber snapshot_seq =
snapshot_cache_[i].load(std::memory_order_acquire);
if (!MaybeUpdateOldCommitMap(evicted.prep_seq, evicted.commit_seq,
snapshot_seq, next_is_larger)) {
break;
}
}
for (auto snapshot_seq_2 : snapshots_) {
if (!MaybeUpdateOldCommitMap(evicted.prep_seq, evicted.commit_seq,
snapshot_seq_2, next_is_larger)) {
break;
}
}
}
}
bool WritePreparedTxnDB::MaybeUpdateOldCommitMap(
const uint64_t& prep_seq, const uint64_t& commit_seq,
const uint64_t& snapshot_seq, const bool next_is_larger = true) {
// If we do not store an entry in old_commit_map_ we assume it is committed in
// all snapshots. If commit_seq <= snapshot_seq, it is considered already in
// the snapshot so we need not to keep the entry around for this snapshot.
if (commit_seq <= snapshot_seq) {
// continue the search if the next snapshot could be smaller than commit_seq
return !next_is_larger;
}
// then snapshot_seq < commit_seq
if (prep_seq <= snapshot_seq) { // overlapping range
WPRecordTick(TXN_OLD_COMMIT_MAP_MUTEX_OVERHEAD);
ROCKS_LOG_WARN(info_log_,
"old_commit_map_mutex_ overhead for %" PRIu64
" commit entry: <%" PRIu64 ",%" PRIu64 ">",
snapshot_seq, prep_seq, commit_seq);
WriteLock wl(&old_commit_map_mutex_);
old_commit_map_empty_.store(false, std::memory_order_release);
auto& vec = old_commit_map_[snapshot_seq];
vec.insert(std::upper_bound(vec.begin(), vec.end(), prep_seq), prep_seq);
// We need to store it once for each overlapping snapshot. Returning true to
// continue the search if there is more overlapping snapshot.
return true;
}
// continue the search if the next snapshot could be larger than prep_seq
return next_is_larger;
}
WritePreparedTxnDB::~WritePreparedTxnDB() {
// At this point there could be running compaction/flush holding a
// SnapshotChecker, which holds a pointer back to WritePreparedTxnDB.
// Make sure those jobs finished before destructing WritePreparedTxnDB.
db_impl_->CancelAllBackgroundWork(true /*wait*/);
}
void SubBatchCounter::InitWithComp(const uint32_t cf) {
auto cmp = comparators_[cf];
keys_[cf] = CFKeys(SetComparator(cmp));
}
void SubBatchCounter::AddKey(const uint32_t cf, const Slice& key) {
CFKeys& cf_keys = keys_[cf];
if (cf_keys.size() == 0) { // just inserted
InitWithComp(cf);
}
auto it = cf_keys.insert(key);
if (it.second == false) { // second is false if a element already existed.
batches_++;
keys_.clear();
InitWithComp(cf);
keys_[cf].insert(key);
}
}
} // namespace rocksdb
#endif // ROCKSDB_LITE