rocksdb/utilities/transactions/write_prepared_txn.cc
Maysam Yabandeh 0ed98bf89e WritePrepared: fix snapshot sequence in rollback (#4851)
Summary:
The rollback algorithm in WritePrepared transactions requires reading the values before the transaction start. Currently it uses the prepare_seq -1 as the snapshot sequence number for the read. This is not correct since the passed sequence number must be for a valid snapshot. The patch fixes it by passing kMaxSequenceNumber instead. This is fine since all the writes done by the aborted transaction will be skipped during the read anyway.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4851

Differential Revision: D13592773

Pulled By: maysamyabandeh

fbshipit-source-id: ff1bf92ea9909d4cccb173bdff49febc0e9eb7a2
2019-01-07 14:57:03 -08:00

442 lines
18 KiB
C++

// 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 "utilities/transactions/write_prepared_txn.h"
#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif
#include <inttypes.h>
#include <map>
#include <set>
#include "db/column_family.h"
#include "db/db_impl.h"
#include "rocksdb/db.h"
#include "rocksdb/status.h"
#include "rocksdb/utilities/transaction_db.h"
#include "util/cast_util.h"
#include "utilities/transactions/pessimistic_transaction.h"
#include "utilities/transactions/write_prepared_txn_db.h"
namespace rocksdb {
struct WriteOptions;
WritePreparedTxn::WritePreparedTxn(WritePreparedTxnDB* txn_db,
const WriteOptions& write_options,
const TransactionOptions& txn_options)
: PessimisticTransaction(txn_db, write_options, txn_options),
wpt_db_(txn_db) {}
void WritePreparedTxn::Initialize(const TransactionOptions& txn_options) {
PessimisticTransaction::Initialize(txn_options);
prepare_batch_cnt_ = 0;
}
Status WritePreparedTxn::Get(const ReadOptions& read_options,
ColumnFamilyHandle* column_family,
const Slice& key, PinnableSlice* pinnable_val) {
auto snapshot = read_options.snapshot;
auto snap_seq =
snapshot != nullptr ? snapshot->GetSequenceNumber() : kMaxSequenceNumber;
SequenceNumber min_uncommitted = 0; // by default disable the optimization
if (snapshot != nullptr) {
min_uncommitted =
static_cast_with_check<const SnapshotImpl, const Snapshot>(snapshot)
->min_uncommitted_;
}
WritePreparedTxnReadCallback callback(wpt_db_, snap_seq, min_uncommitted);
return write_batch_.GetFromBatchAndDB(db_, read_options, column_family, key,
pinnable_val, &callback);
}
Iterator* WritePreparedTxn::GetIterator(const ReadOptions& options) {
// Make sure to get iterator from WritePrepareTxnDB, not the root db.
Iterator* db_iter = wpt_db_->NewIterator(options);
assert(db_iter);
return write_batch_.NewIteratorWithBase(db_iter);
}
Iterator* WritePreparedTxn::GetIterator(const ReadOptions& options,
ColumnFamilyHandle* column_family) {
// Make sure to get iterator from WritePrepareTxnDB, not the root db.
Iterator* db_iter = wpt_db_->NewIterator(options, column_family);
assert(db_iter);
return write_batch_.NewIteratorWithBase(column_family, db_iter);
}
Status WritePreparedTxn::PrepareInternal() {
WriteOptions write_options = write_options_;
write_options.disableWAL = false;
const bool WRITE_AFTER_COMMIT = true;
WriteBatchInternal::MarkEndPrepare(GetWriteBatch()->GetWriteBatch(), name_,
!WRITE_AFTER_COMMIT);
// For each duplicate key we account for a new sub-batch
prepare_batch_cnt_ = GetWriteBatch()->SubBatchCnt();
// AddPrepared better to be called in the pre-release callback otherwise there
// is a non-zero chance of max advancing prepare_seq and readers assume the
// data as committed.
// Also having it in the PreReleaseCallback allows in-order addition of
// prepared entries to PrepareHeap and hence enables an optimization. Refer to
// SmallestUnCommittedSeq for more details.
AddPreparedCallback add_prepared_callback(
wpt_db_, prepare_batch_cnt_,
db_impl_->immutable_db_options().two_write_queues);
const bool DISABLE_MEMTABLE = true;
uint64_t seq_used = kMaxSequenceNumber;
Status s = db_impl_->WriteImpl(
write_options, GetWriteBatch()->GetWriteBatch(),
/*callback*/ nullptr, &log_number_, /*log ref*/ 0, !DISABLE_MEMTABLE,
&seq_used, prepare_batch_cnt_, &add_prepared_callback);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
auto prepare_seq = seq_used;
SetId(prepare_seq);
return s;
}
Status WritePreparedTxn::CommitWithoutPrepareInternal() {
// For each duplicate key we account for a new sub-batch
const size_t batch_cnt = GetWriteBatch()->SubBatchCnt();
return CommitBatchInternal(GetWriteBatch()->GetWriteBatch(), batch_cnt);
}
Status WritePreparedTxn::CommitBatchInternal(WriteBatch* batch,
size_t batch_cnt) {
return wpt_db_->WriteInternal(write_options_, batch, batch_cnt, this);
}
Status WritePreparedTxn::CommitInternal() {
ROCKS_LOG_DETAILS(db_impl_->immutable_db_options().info_log,
"CommitInternal prepare_seq: %" PRIu64, GetID());
// We take the commit-time batch and append the Commit marker.
// The Memtable will ignore the Commit marker in non-recovery mode
WriteBatch* working_batch = GetCommitTimeWriteBatch();
const bool empty = working_batch->Count() == 0;
WriteBatchInternal::MarkCommit(working_batch, name_);
const bool for_recovery = use_only_the_last_commit_time_batch_for_recovery_;
if (!empty && for_recovery) {
// When not writing to memtable, we can still cache the latest write batch.
// The cached batch will be written to memtable in WriteRecoverableState
// during FlushMemTable
WriteBatchInternal::SetAsLastestPersistentState(working_batch);
}
auto prepare_seq = GetId();
const bool includes_data = !empty && !for_recovery;
assert(prepare_batch_cnt_);
size_t commit_batch_cnt = 0;
if (UNLIKELY(includes_data)) {
ROCKS_LOG_WARN(db_impl_->immutable_db_options().info_log,
"Duplicate key overhead");
SubBatchCounter counter(*wpt_db_->GetCFComparatorMap());
auto s = working_batch->Iterate(&counter);
assert(s.ok());
commit_batch_cnt = counter.BatchCount();
}
const bool disable_memtable = !includes_data;
const bool do_one_write =
!db_impl_->immutable_db_options().two_write_queues || disable_memtable;
const bool publish_seq = do_one_write;
// Note: CommitTimeWriteBatch does not need AddPrepared since it is written to
// DB in one shot. min_uncommitted still works since it requires capturing
// data that is written to DB but not yet committed, while
// CommitTimeWriteBatch commits with PreReleaseCallback.
WritePreparedCommitEntryPreReleaseCallback update_commit_map(
wpt_db_, db_impl_, prepare_seq, prepare_batch_cnt_, commit_batch_cnt,
publish_seq);
uint64_t seq_used = kMaxSequenceNumber;
// Since the prepared batch is directly written to memtable, there is already
// a connection between the memtable and its WAL, so there is no need to
// redundantly reference the log that contains the prepared data.
const uint64_t zero_log_number = 0ull;
size_t batch_cnt = UNLIKELY(commit_batch_cnt) ? commit_batch_cnt : 1;
auto s = db_impl_->WriteImpl(write_options_, working_batch, nullptr, nullptr,
zero_log_number, disable_memtable, &seq_used,
batch_cnt, &update_commit_map);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
if (LIKELY(do_one_write || !s.ok())) {
if (LIKELY(s.ok())) {
// Note RemovePrepared should be called after WriteImpl that publishsed
// the seq. Otherwise SmallestUnCommittedSeq optimization breaks.
wpt_db_->RemovePrepared(prepare_seq, prepare_batch_cnt_);
}
return s;
} // else do the 2nd write to publish seq
// Note: the 2nd write comes with a performance penality. So if we have too
// many of commits accompanied with ComitTimeWriteBatch and yet we cannot
// enable use_only_the_last_commit_time_batch_for_recovery_ optimization,
// two_write_queues should be disabled to avoid many additional writes here.
class PublishSeqPreReleaseCallback : public PreReleaseCallback {
public:
explicit PublishSeqPreReleaseCallback(DBImpl* db_impl)
: db_impl_(db_impl) {}
virtual Status Callback(SequenceNumber seq, bool is_mem_disabled) override {
#ifdef NDEBUG
(void)is_mem_disabled;
#endif
assert(is_mem_disabled);
assert(db_impl_->immutable_db_options().two_write_queues);
db_impl_->SetLastPublishedSequence(seq);
return Status::OK();
}
private:
DBImpl* db_impl_;
} publish_seq_callback(db_impl_);
WriteBatch empty_batch;
empty_batch.PutLogData(Slice());
// In the absence of Prepare markers, use Noop as a batch separator
WriteBatchInternal::InsertNoop(&empty_batch);
const bool DISABLE_MEMTABLE = true;
const size_t ONE_BATCH = 1;
const uint64_t NO_REF_LOG = 0;
s = db_impl_->WriteImpl(write_options_, &empty_batch, nullptr, nullptr,
NO_REF_LOG, DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
&publish_seq_callback);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
// Note RemovePrepared should be called after WriteImpl that publishsed the
// seq. Otherwise SmallestUnCommittedSeq optimization breaks.
wpt_db_->RemovePrepared(prepare_seq, prepare_batch_cnt_);
return s;
}
Status WritePreparedTxn::RollbackInternal() {
ROCKS_LOG_WARN(db_impl_->immutable_db_options().info_log,
"RollbackInternal prepare_seq: %" PRIu64, GetId());
WriteBatch rollback_batch;
assert(GetId() != kMaxSequenceNumber);
assert(GetId() > 0);
auto cf_map_shared_ptr = wpt_db_->GetCFHandleMap();
auto cf_comp_map_shared_ptr = wpt_db_->GetCFComparatorMap();
auto read_at_seq = kMaxSequenceNumber;
struct RollbackWriteBatchBuilder : public WriteBatch::Handler {
DBImpl* db_;
ReadOptions roptions;
WritePreparedTxnReadCallback 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, WritePreparedTxnDB* wpt_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(wpt_db, snap_seq,
0), // 0 disables 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 it = cf_keys.insert(key);
if (it.second ==
false) { // second is false if a element already existed.
return s;
}
PinnableSlice pinnable_val;
bool not_used;
auto cf_handle = handles_[cf];
s = db_->GetImpl(roptions, cf_handle, key, &pinnable_val, &not_used,
&callback);
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();
}
}
Status MarkNoop(bool) override { return Status::OK(); }
Status MarkBeginPrepare(bool) override { return Status::OK(); }
Status MarkEndPrepare(const Slice&) override { return Status::OK(); }
Status MarkCommit(const Slice&) override { return Status::OK(); }
Status MarkRollback(const Slice&) override {
return Status::InvalidArgument();
}
protected:
virtual bool WriteAfterCommit() const override { return false; }
} rollback_handler(db_impl_, wpt_db_, read_at_seq, &rollback_batch,
*cf_comp_map_shared_ptr.get(), *cf_map_shared_ptr.get(),
wpt_db_->txn_db_options_.rollback_merge_operands);
auto s = GetWriteBatch()->GetWriteBatch()->Iterate(&rollback_handler);
assert(s.ok());
if (!s.ok()) {
return s;
}
// The Rollback marker will be used as a batch separator
WriteBatchInternal::MarkRollback(&rollback_batch, name_);
bool do_one_write = !db_impl_->immutable_db_options().two_write_queues;
const bool DISABLE_MEMTABLE = true;
const uint64_t NO_REF_LOG = 0;
uint64_t seq_used = kMaxSequenceNumber;
const size_t ONE_BATCH = 1;
// We commit the rolled back prepared batches. ALthough this is
// counter-intuitive, i) it is safe to do so, since the prepared batches are
// already canceled out by the rollback batch, ii) adding the commit entry to
// CommitCache will allow us to benefit from the existing mechanism in
// CommitCache that keeps an entry evicted due to max advance and yet overlaps
// with a live snapshot around so that the live snapshot properly skips the
// entry even if its prepare seq is lower than max_evicted_seq_.
WritePreparedCommitEntryPreReleaseCallback update_commit_map(
wpt_db_, db_impl_, GetId(), prepare_batch_cnt_, ONE_BATCH);
// Note: the rollback batch does not need AddPrepared since it is written to
// DB in one shot. min_uncommitted still works since it requires capturing
// data that is written to DB but not yet committed, while
// the roolback batch commits with PreReleaseCallback.
s = db_impl_->WriteImpl(write_options_, &rollback_batch, nullptr, nullptr,
NO_REF_LOG, !DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
do_one_write ? &update_commit_map : nullptr);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
if (!s.ok()) {
return s;
}
if (do_one_write) {
wpt_db_->RemovePrepared(GetId(), prepare_batch_cnt_);
return s;
} // else do the 2nd write for commit
uint64_t& prepare_seq = seq_used;
ROCKS_LOG_DETAILS(db_impl_->immutable_db_options().info_log,
"RollbackInternal 2nd write prepare_seq: %" PRIu64,
prepare_seq);
// Commit the batch by writing an empty batch to the queue that will release
// the commit sequence number to readers.
const size_t ZERO_COMMITS = 0;
WritePreparedCommitEntryPreReleaseCallback update_commit_map_with_prepare(
wpt_db_, db_impl_, prepare_seq, ONE_BATCH, ZERO_COMMITS);
WriteBatch empty_batch;
empty_batch.PutLogData(Slice());
// In the absence of Prepare markers, use Noop as a batch separator
WriteBatchInternal::InsertNoop(&empty_batch);
s = db_impl_->WriteImpl(write_options_, &empty_batch, nullptr, nullptr,
NO_REF_LOG, DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
&update_commit_map_with_prepare);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
// Mark the txn as rolled back
uint64_t& rollback_seq = seq_used;
if (s.ok()) {
// Note: it is safe to do it after PreReleaseCallback via WriteImpl since
// all the writes by the prpared batch are already blinded by the rollback
// batch. The only reason we commit the prepared batch here is to benefit
// from the existing mechanism in CommitCache that takes care of the rare
// cases that the prepare seq is visible to a snsapshot but max evicted seq
// advances that prepare seq.
for (size_t i = 0; i < prepare_batch_cnt_; i++) {
wpt_db_->AddCommitted(GetId() + i, rollback_seq);
}
wpt_db_->RemovePrepared(GetId(), prepare_batch_cnt_);
}
return s;
}
Status WritePreparedTxn::ValidateSnapshot(ColumnFamilyHandle* column_family,
const Slice& key,
SequenceNumber* tracked_at_seq) {
assert(snapshot_);
SequenceNumber min_uncommitted =
static_cast_with_check<const SnapshotImpl, const Snapshot>(
snapshot_.get())
->min_uncommitted_;
SequenceNumber snap_seq = snapshot_->GetSequenceNumber();
// tracked_at_seq is either max or the last snapshot with which this key was
// trackeed so there is no need to apply the IsInSnapshot to this comparison
// here as tracked_at_seq is not a prepare seq.
if (*tracked_at_seq <= snap_seq) {
// If the key has been previous validated at a sequence number earlier
// than the curent snapshot's sequence number, we already know it has not
// been modified.
return Status::OK();
}
*tracked_at_seq = snap_seq;
ColumnFamilyHandle* cfh =
column_family ? column_family : db_impl_->DefaultColumnFamily();
WritePreparedTxnReadCallback snap_checker(wpt_db_, snap_seq, min_uncommitted);
return TransactionUtil::CheckKeyForConflicts(db_impl_, cfh, key.ToString(),
snap_seq, false /* cache_only */,
&snap_checker);
}
void WritePreparedTxn::SetSnapshot() {
// 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 = wpt_db_->SmallestUnCommittedSeq();
const bool FOR_WW_CONFLICT_CHECK = true;
SnapshotImpl* snapshot = dbimpl_->GetSnapshotImpl(FOR_WW_CONFLICT_CHECK);
assert(snapshot);
wpt_db_->EnhanceSnapshot(snapshot, min_uncommitted);
SetSnapshotInternal(snapshot);
}
Status WritePreparedTxn::RebuildFromWriteBatch(WriteBatch* src_batch) {
auto ret = PessimisticTransaction::RebuildFromWriteBatch(src_batch);
prepare_batch_cnt_ = GetWriteBatch()->SubBatchCnt();
return ret;
}
} // namespace rocksdb
#endif // ROCKSDB_LITE