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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).
#include "utilities/transactions/write_unprepared_txn_db.h"
#include "db/arena_wrapped_db_iter.h"
#include "rocksdb/utilities/transaction_db.h"
#include "util/cast_util.h"
namespace ROCKSDB_NAMESPACE {
// Instead of reconstructing a Transaction object, and calling rollback on it,
// we can be more efficient with RollbackRecoveredTransaction by skipping
// unnecessary steps (eg. updating CommitMap, reconstructing keyset)
Status WriteUnpreparedTxnDB::RollbackRecoveredTransaction(
const DBImpl::RecoveredTransaction* rtxn) {
// TODO(lth): Reduce duplicate code with WritePrepared rollback logic.
assert(rtxn->unprepared_);
auto cf_map_shared_ptr = WritePreparedTxnDB::GetCFHandleMap();
auto cf_comp_map_shared_ptr = WritePreparedTxnDB::GetCFComparatorMap();
// In theory we could write with disableWAL = true during recovery, and
// assume that if we crash again during recovery, we can just replay from
// the very beginning. Unfortunately, the XIDs from the application may not
// necessarily be unique across restarts, potentially leading to situations
// like this:
//
// BEGIN_PREPARE(unprepared) Put(a) END_PREPARE(xid = 1)
// -- crash and recover with Put(a) rolled back as it was not prepared
// BEGIN_PREPARE(prepared) Put(b) END_PREPARE(xid = 1)
// COMMIT(xid = 1)
// -- crash and recover with both a, b
//
// We could just write the rollback marker, but then we would have to extend
// MemTableInserter during recovery to actually do writes into the DB
// instead of just dropping the in-memory write batch.
//
WriteOptions w_options;
class InvalidSnapshotReadCallback : public ReadCallback {
public:
InvalidSnapshotReadCallback(SequenceNumber snapshot)
: ReadCallback(snapshot) {}
inline bool IsVisibleFullCheck(SequenceNumber) override {
// The seq provided as snapshot is the seq right before we have locked and
// wrote to it, so whatever is there, it is committed.
return true;
}
// Ignore the refresh request since we are confident that our snapshot seq
// is not going to be affected by concurrent compactions (not enabled yet.)
void Refresh(SequenceNumber) override {}
};
// Iterate starting with largest sequence number.
for (auto it = rtxn->batches_.rbegin(); it != rtxn->batches_.rend(); ++it) {
auto last_visible_txn = it->first - 1;
const auto& batch = it->second.batch_;
WriteBatch rollback_batch(0 /* reserved_bytes */, 0 /* max_bytes */,
w_options.protection_bytes_per_key,
0 /* default_cf_ts_sz */);
struct RollbackWriteBatchBuilder : public WriteBatch::Handler {
DBImpl* db_;
ReadOptions roptions;
InvalidSnapshotReadCallback callback;
WriteBatch* rollback_batch_;
std::map<uint32_t, const Comparator*>& comparators_;
std::map<uint32_t, ColumnFamilyHandle*>& handles_;
using CFKeys = std::set<Slice, SetComparator>;
std::map<uint32_t, CFKeys> keys_;
bool rollback_merge_operands_;
RollbackWriteBatchBuilder(
DBImpl* db, SequenceNumber snap_seq, WriteBatch* dst_batch,
std::map<uint32_t, const Comparator*>& comparators,
std::map<uint32_t, ColumnFamilyHandle*>& handles,
bool rollback_merge_operands)
: db_(db),
callback(snap_seq),
// disable min_uncommitted optimization
rollback_batch_(dst_batch),
comparators_(comparators),
handles_(handles),
rollback_merge_operands_(rollback_merge_operands) {}
Status Rollback(uint32_t cf, const Slice& key) {
Status s;
CFKeys& cf_keys = keys_[cf];
if (cf_keys.size() == 0) { // just inserted
auto cmp = comparators_[cf];
keys_[cf] = CFKeys(SetComparator(cmp));
}
auto res = cf_keys.insert(key);
if (res.second ==
false) { // second is false if a element already existed.
return s;
}
PinnableSlice pinnable_val;
bool not_used;
auto cf_handle = handles_[cf];
DBImpl::GetImplOptions get_impl_options;
get_impl_options.column_family = cf_handle;
get_impl_options.value = &pinnable_val;
get_impl_options.value_found = &not_used;
get_impl_options.callback = &callback;
s = db_->GetImpl(roptions, key, get_impl_options);
assert(s.ok() || s.IsNotFound());
if (s.ok()) {
s = rollback_batch_->Put(cf_handle, key, pinnable_val);
assert(s.ok());
} else if (s.IsNotFound()) {
// There has been no readable value before txn. By adding a delete we
// make sure that there will be none afterwards either.
s = rollback_batch_->Delete(cf_handle, key);
assert(s.ok());
} else {
// Unexpected status. Return it to the user.
}
return s;
}
Status PutCF(uint32_t cf, const Slice& key,
const Slice& /*val*/) override {
return Rollback(cf, key);
}
Status DeleteCF(uint32_t cf, const Slice& key) override {
return Rollback(cf, key);
}
Status SingleDeleteCF(uint32_t cf, const Slice& key) override {
return Rollback(cf, key);
}
Status MergeCF(uint32_t cf, const Slice& key,
const Slice& /*val*/) override {
if (rollback_merge_operands_) {
return Rollback(cf, key);
} else {
return Status::OK();
}
}
// Recovered batches do not contain 2PC markers.
Status MarkNoop(bool) override { return Status::InvalidArgument(); }
Status MarkBeginPrepare(bool) override {
return Status::InvalidArgument();
}
Status MarkEndPrepare(const Slice&) override {
return Status::InvalidArgument();
}
Status MarkCommit(const Slice&) override {
return Status::InvalidArgument();
}
Status MarkRollback(const Slice&) override {
return Status::InvalidArgument();
}
} rollback_handler(db_impl_, last_visible_txn, &rollback_batch,
*cf_comp_map_shared_ptr.get(), *cf_map_shared_ptr.get(),
txn_db_options_.rollback_merge_operands);
auto s = batch->Iterate(&rollback_handler);
if (!s.ok()) {
return s;
}
// The Rollback marker will be used as a batch separator
s = WriteBatchInternal::MarkRollback(&rollback_batch, rtxn->name_);
if (!s.ok()) {
return s;
}
const uint64_t kNoLogRef = 0;
const bool kDisableMemtable = true;
const size_t kOneBatch = 1;
uint64_t seq_used = kMaxSequenceNumber;
s = db_impl_->WriteImpl(w_options, &rollback_batch, nullptr, nullptr,
kNoLogRef, !kDisableMemtable, &seq_used, kOneBatch);
if (!s.ok()) {
return s;
}
// If two_write_queues, we must manually release the sequence number to
// readers.
if (db_impl_->immutable_db_options().two_write_queues) {
db_impl_->SetLastPublishedSequence(seq_used);
}
}
return Status::OK();
}
Status WriteUnpreparedTxnDB::Initialize(
const std::vector<size_t>& compaction_enabled_cf_indices,
const std::vector<ColumnFamilyHandle*>& handles) {
// TODO(lth): Reduce code duplication in this function.
auto dbimpl = static_cast_with_check<DBImpl>(GetRootDB());
assert(dbimpl != nullptr);
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,
size_t /*index*/, size_t /*total*/) override {
assert(!is_mem_disabled);
db_->AddCommitted(commit_seq, commit_seq);
return Status::OK();
}
private:
WritePreparedTxnDB* db_;
};
db_impl_->SetRecoverableStatePreReleaseCallback(
new CommitSubBatchPreReleaseCallback(this));
// PessimisticTransactionDB::Initialize
for (auto cf_ptr : handles) {
AddColumnFamily(cf_ptr);
}
// Verify cf options
for (auto handle : handles) {
ColumnFamilyDescriptor cfd;
Status s = handle->GetDescriptor(&cfd);
if (!s.ok()) {
return s;
}
s = VerifyCFOptions(cfd.options);
if (!s.ok()) {
return s;
}
}
// Re-enable compaction for the column families that initially had
// compaction enabled.
std::vector<ColumnFamilyHandle*> compaction_enabled_cf_handles;
compaction_enabled_cf_handles.reserve(compaction_enabled_cf_indices.size());
for (auto index : compaction_enabled_cf_indices) {
compaction_enabled_cf_handles.push_back(handles[index]);
}
// create 'real' transactions from recovered shell transactions
auto rtxns = dbimpl->recovered_transactions();
std::map<SequenceNumber, SequenceNumber> ordered_seq_cnt;
for (auto rtxn : rtxns) {
auto recovered_trx = rtxn.second;
assert(recovered_trx);
assert(recovered_trx->batches_.size() >= 1);
assert(recovered_trx->name_.length());
// We can only rollback transactions after AdvanceMaxEvictedSeq is called,
// but AddPrepared must occur before AdvanceMaxEvictedSeq, which is why
// two iterations is required.
if (recovered_trx->unprepared_) {
continue;
}
WriteOptions w_options;
w_options.sync = true;
TransactionOptions t_options;
auto first_log_number = recovered_trx->batches_.begin()->second.log_number_;
auto first_seq = recovered_trx->batches_.begin()->first;
auto last_prepare_batch_cnt =
recovered_trx->batches_.begin()->second.batch_cnt_;
Transaction* real_trx = BeginTransaction(w_options, t_options, nullptr);
assert(real_trx);
auto wupt = static_cast_with_check<WriteUnpreparedTxn>(real_trx);
wupt->recovered_txn_ = true;
real_trx->SetLogNumber(first_log_number);
real_trx->SetId(first_seq);
Status s = real_trx->SetName(recovered_trx->name_);
if (!s.ok()) {
return s;
}
wupt->prepare_batch_cnt_ = last_prepare_batch_cnt;
for (auto batch : recovered_trx->batches_) {
const auto& seq = batch.first;
const auto& batch_info = batch.second;
auto cnt = batch_info.batch_cnt_ ? batch_info.batch_cnt_ : 1;
assert(batch_info.log_number_);
ordered_seq_cnt[seq] = cnt;
assert(wupt->unprep_seqs_.count(seq) == 0);
wupt->unprep_seqs_[seq] = cnt;
s = wupt->RebuildFromWriteBatch(batch_info.batch_);
assert(s.ok());
if (!s.ok()) {
return s;
}
}
const bool kClear = true;
wupt->InitWriteBatch(kClear);
real_trx->SetState(Transaction::PREPARED);
if (!s.ok()) {
return s;
}
}
// AddPrepared must be called in order
for (auto seq_cnt : ordered_seq_cnt) {
auto seq = seq_cnt.first;
auto cnt = seq_cnt.second;
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);
}
Status s;
// Rollback unprepared transactions.
for (auto rtxn : rtxns) {
auto recovered_trx = rtxn.second;
if (recovered_trx->unprepared_) {
s = RollbackRecoveredTransaction(recovered_trx);
if (!s.ok()) {
return s;
}
continue;
}
}
if (s.ok()) {
dbimpl->DeleteAllRecoveredTransactions();
// Compaction should start only after max_evicted_seq_ is set AND recovered
// transactions are either added to PrepareHeap or rolled back.
s = EnableAutoCompaction(compaction_enabled_cf_handles);
}
return s;
}
Transaction* WriteUnpreparedTxnDB::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 WriteUnpreparedTxn(this, write_options, txn_options);
}
}
// Struct to hold ownership of snapshot and read callback for iterator cleanup.
struct WriteUnpreparedTxnDB::IteratorState {
IteratorState(WritePreparedTxnDB* txn_db, SequenceNumber sequence,
std::shared_ptr<ManagedSnapshot> s,
SequenceNumber min_uncommitted, WriteUnpreparedTxn* txn)
: callback(txn_db, sequence, min_uncommitted, txn->unprep_seqs_,
kBackedByDBSnapshot),
snapshot(s) {}
SequenceNumber MaxVisibleSeq() { return callback.max_visible_seq(); }
WriteUnpreparedTxnReadCallback callback;
std::shared_ptr<ManagedSnapshot> snapshot;
};
namespace {
static void CleanupWriteUnpreparedTxnDBIterator(void* arg1, void* /*arg2*/) {
delete reinterpret_cast<WriteUnpreparedTxnDB::IteratorState*>(arg1);
}
} // anonymous namespace
Iterator* WriteUnpreparedTxnDB::NewIterator(const ReadOptions& options,
ColumnFamilyHandle* column_family,
WriteUnpreparedTxn* txn) {
if (options.io_activity != Env::IOActivity::kUnknown) {
return NewErrorIterator(Status::InvalidArgument(
"Cannot call NewIterator with `ReadOptions::io_activity` != "
"`Env::IOActivity::kUnknown`"));
}
// TODO(lth): Refactor so that this logic is shared with WritePrepared.
constexpr bool expose_blob_index = false;
constexpr bool allow_refresh = false;
std::shared_ptr<ManagedSnapshot> own_snapshot = nullptr;
SequenceNumber snapshot_seq = kMaxSequenceNumber;
SequenceNumber min_uncommitted = 0;
// Currently, the Prev() iterator logic does not work well without snapshot
// validation. The logic simply iterates through values of a key in
// ascending seqno order, stopping at the first non-visible value and
// returning the last visible value.
//
// For example, if snapshot sequence is 3, and we have the following keys:
// foo: v1 1
// foo: v2 2
// foo: v3 3
// foo: v4 4
// foo: v5 5
//
// Then 1, 2, 3 will be visible, but 4 will be non-visible, so we return v3,
// which is the last visible value.
//
// For unprepared transactions, if we have snap_seq = 3, but the current
// transaction has unprep_seq 5, then returning the first non-visible value
// would be incorrect, as we should return v5, and not v3. The problem is that
// there are committed values at snapshot_seq < commit_seq < unprep_seq.
//
// Snapshot validation can prevent this problem by ensuring that no committed
// values exist at snapshot_seq < commit_seq, and thus any value with a
// sequence number greater than snapshot_seq must be unprepared values. For
// example, if the transaction had a snapshot at 3, then snapshot validation
// would be performed during the Put(v5) call. It would find v4, and the Put
// would fail with snapshot validation failure.
//
// TODO(lth): Improve Prev() logic to continue iterating until
// max_visible_seq, and then return the last visible value, so that this
// restriction can be lifted.
const Snapshot* snapshot = nullptr;
if (options.snapshot == nullptr) {
snapshot = GetSnapshot();
own_snapshot = std::make_shared<ManagedSnapshot>(db_impl_, snapshot);
} else {
snapshot = options.snapshot;
}
snapshot_seq = snapshot->GetSequenceNumber();
assert(snapshot_seq != kMaxSequenceNumber);
// Iteration is safe as long as largest_validated_seq <= snapshot_seq. We are
// guaranteed that for keys that were modified by this transaction (and thus
// might have unprepared values), no committed values exist at
// largest_validated_seq < commit_seq (or the contrapositive: any committed
// value must exist at commit_seq <= largest_validated_seq). This implies
// that commit_seq <= largest_validated_seq <= snapshot_seq or commit_seq <=
// snapshot_seq. As explained above, the problem with Prev() only happens when
// snapshot_seq < commit_seq.
//
// For keys that were not modified by this transaction, largest_validated_seq_
// is meaningless, and Prev() should just work with the existing visibility
// logic.
if (txn->largest_validated_seq_ > snapshot->GetSequenceNumber() &&
!txn->unprep_seqs_.empty()) {
ROCKS_LOG_ERROR(info_log_,
"WriteUnprepared iterator creation failed since the "
"transaction has performed unvalidated writes");
return nullptr;
}
min_uncommitted =
static_cast_with_check<const SnapshotImpl>(snapshot)->min_uncommitted_;
auto* cfd =
static_cast_with_check<ColumnFamilyHandleImpl>(column_family)->cfd();
auto* state =
new IteratorState(this, snapshot_seq, own_snapshot, min_uncommitted, txn);
auto* db_iter = db_impl_->NewIteratorImpl(
options, cfd, state->MaxVisibleSeq(), &state->callback, expose_blob_index,
allow_refresh);
db_iter->RegisterCleanup(CleanupWriteUnpreparedTxnDBIterator, state, nullptr);
return db_iter;
}
} // namespace ROCKSDB_NAMESPACE