rocksdb/utilities/transactions/write_unprepared_txn.cc
Maysam Yabandeh f3a99e8a4d WritePrepared: Report released snapshots in IsInSnapshot (#4856)
Summary:
Previously IsInSnapshot assumed that the snapshot is valid at the time that the function is called. However there are cases where that might not be valid. Example is background compactions where the compaction algorithm operates with a list of snapshots some of which might be released by the time they are being passed to IsInSnapshot. The patch make two changes to enable the caller to tell difference: i) any live snapshot below max is added to max_committed_seq_, which allows IsInSnapshot to confidently tell whether the passed snapshot is invalid if it below max, ii) extends IsInSnapshot API with a "released" variable that is set true when IsInSnapshot find no such snapshot below max and also find no other way to give a certain return value. In such cases the return value is true but the caller should also check the "released" boolean after the call.
In short here is the changes in the API:
i) If the snapshot is valid, no change is required.
ii) If the snapshot might be invalid, a reference to "released" boolean must be passed to IsInSnapshot.
ii-a) If snapshot is above max, IsInSnapshot can figure the return valid using the commit cache.
ii-b) otherwise if snapshot is in old_commit_map_, IsInSnapshot can use that to tell if value was visible to the snapshot.
ii-c) otherwise it sets "released" to true and returns true as well.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4856

Differential Revision: D13599847

Pulled By: maysamyabandeh

fbshipit-source-id: 1752be28667f886a1efec8cae5714b9b7a8f1e0f
2019-01-08 14:47:29 -08:00

525 lines
20 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_unprepared_txn.h"
#include "db/db_impl.h"
#include "util/cast_util.h"
#include "utilities/transactions/write_unprepared_txn_db.h"
#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif
namespace rocksdb {
bool WriteUnpreparedTxnReadCallback::IsVisible(SequenceNumber seq) {
auto unprep_seqs = txn_->GetUnpreparedSequenceNumbers();
// Since unprep_seqs maps prep_seq => prepare_batch_cnt, to check if seq is
// in unprep_seqs, we have to check if seq is equal to prep_seq or any of
// the prepare_batch_cnt seq nums after it.
//
// TODO(lth): Can be optimized with std::lower_bound if unprep_seqs is
// large.
for (const auto& it : unprep_seqs) {
if (it.first <= seq && seq < it.first + it.second) {
return true;
}
}
return db_->IsInSnapshot(seq, snapshot_, min_uncommitted_);
}
SequenceNumber WriteUnpreparedTxnReadCallback::MaxUnpreparedSequenceNumber() {
auto unprep_seqs = txn_->GetUnpreparedSequenceNumbers();
if (unprep_seqs.size()) {
return unprep_seqs.rbegin()->first + unprep_seqs.rbegin()->second - 1;
}
return 0;
}
WriteUnpreparedTxn::WriteUnpreparedTxn(WriteUnpreparedTxnDB* txn_db,
const WriteOptions& write_options,
const TransactionOptions& txn_options)
: WritePreparedTxn(txn_db, write_options, txn_options), wupt_db_(txn_db) {
max_write_batch_size_ = txn_options.max_write_batch_size;
// We set max bytes to zero so that we don't get a memory limit error.
// Instead of trying to keep write batch strictly under the size limit, we
// just flush to DB when the limit is exceeded in write unprepared, to avoid
// having retry logic. This also allows very big key-value pairs that exceed
// max bytes to succeed.
write_batch_.SetMaxBytes(0);
}
WriteUnpreparedTxn::~WriteUnpreparedTxn() {
if (!unprep_seqs_.empty()) {
assert(log_number_ > 0);
assert(GetId() > 0);
assert(!name_.empty());
// We should rollback regardless of GetState, but some unit tests that
// test crash recovery run the destructor assuming that rollback does not
// happen, so that rollback during recovery can be exercised.
if (GetState() == STARTED) {
auto s __attribute__((__unused__)) = RollbackInternal();
// TODO(lth): Better error handling.
assert(s.ok());
dbimpl_->logs_with_prep_tracker()->MarkLogAsHavingPrepSectionFlushed(
log_number_);
}
}
}
void WriteUnpreparedTxn::Initialize(const TransactionOptions& txn_options) {
PessimisticTransaction::Initialize(txn_options);
max_write_batch_size_ = txn_options.max_write_batch_size;
write_batch_.SetMaxBytes(0);
unprep_seqs_.clear();
write_set_keys_.clear();
}
Status WriteUnpreparedTxn::Put(ColumnFamilyHandle* column_family,
const Slice& key, const Slice& value,
const bool assume_tracked) {
Status s = MaybeFlushWriteBatchToDB();
if (!s.ok()) {
return s;
}
return TransactionBaseImpl::Put(column_family, key, value, assume_tracked);
}
Status WriteUnpreparedTxn::Put(ColumnFamilyHandle* column_family,
const SliceParts& key, const SliceParts& value,
const bool assume_tracked) {
Status s = MaybeFlushWriteBatchToDB();
if (!s.ok()) {
return s;
}
return TransactionBaseImpl::Put(column_family, key, value, assume_tracked);
}
Status WriteUnpreparedTxn::Merge(ColumnFamilyHandle* column_family,
const Slice& key, const Slice& value,
const bool assume_tracked) {
Status s = MaybeFlushWriteBatchToDB();
if (!s.ok()) {
return s;
}
return TransactionBaseImpl::Merge(column_family, key, value, assume_tracked);
}
Status WriteUnpreparedTxn::Delete(ColumnFamilyHandle* column_family,
const Slice& key, const bool assume_tracked) {
Status s = MaybeFlushWriteBatchToDB();
if (!s.ok()) {
return s;
}
return TransactionBaseImpl::Delete(column_family, key, assume_tracked);
}
Status WriteUnpreparedTxn::Delete(ColumnFamilyHandle* column_family,
const SliceParts& key,
const bool assume_tracked) {
Status s = MaybeFlushWriteBatchToDB();
if (!s.ok()) {
return s;
}
return TransactionBaseImpl::Delete(column_family, key, assume_tracked);
}
Status WriteUnpreparedTxn::SingleDelete(ColumnFamilyHandle* column_family,
const Slice& key,
const bool assume_tracked) {
Status s = MaybeFlushWriteBatchToDB();
if (!s.ok()) {
return s;
}
return TransactionBaseImpl::SingleDelete(column_family, key, assume_tracked);
}
Status WriteUnpreparedTxn::SingleDelete(ColumnFamilyHandle* column_family,
const SliceParts& key,
const bool assume_tracked) {
Status s = MaybeFlushWriteBatchToDB();
if (!s.ok()) {
return s;
}
return TransactionBaseImpl::SingleDelete(column_family, key, assume_tracked);
}
Status WriteUnpreparedTxn::MaybeFlushWriteBatchToDB() {
const bool kPrepared = true;
Status s;
bool needs_mark = (log_number_ == 0);
if (max_write_batch_size_ != 0 &&
write_batch_.GetDataSize() > max_write_batch_size_) {
assert(GetState() != PREPARED);
s = FlushWriteBatchToDB(!kPrepared);
if (s.ok()) {
assert(log_number_ > 0);
// This is done to prevent WAL files after log_number_ from being
// deleted, because they could potentially contain unprepared batches.
if (needs_mark) {
dbimpl_->logs_with_prep_tracker()->MarkLogAsContainingPrepSection(
log_number_);
}
}
}
return s;
}
void WriteUnpreparedTxn::UpdateWriteKeySet(uint32_t cfid, const Slice& key) {
// TODO(lth): write_set_keys_ can just be a std::string instead of a vector.
write_set_keys_[cfid].push_back(key.ToString());
}
Status WriteUnpreparedTxn::FlushWriteBatchToDB(bool prepared) {
if (name_.empty()) {
return Status::InvalidArgument("Cannot write to DB without SetName.");
}
// Update write_key_set_ for rollback purposes.
KeySetBuilder keyset_handler(
this, wupt_db_->txn_db_options_.rollback_merge_operands);
auto s = GetWriteBatch()->GetWriteBatch()->Iterate(&keyset_handler);
assert(s.ok());
if (!s.ok()) {
return s;
}
// TODO(lth): Reduce duplicate code with WritePrepared prepare logic.
WriteOptions write_options = write_options_;
write_options.disableWAL = false;
const bool WRITE_AFTER_COMMIT = true;
// MarkEndPrepare will change Noop marker to the appropriate marker.
WriteBatchInternal::MarkEndPrepare(GetWriteBatch()->GetWriteBatch(), name_,
!WRITE_AFTER_COMMIT, !prepared);
// 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;
// log_number_ should refer to the oldest log containing uncommitted data
// from the current transaction. This means that if log_number_ is set,
// WriteImpl should not overwrite that value, so set log_used to nullptr if
// log_number_ is already set.
uint64_t* log_used = log_number_ ? nullptr : &log_number_;
s = db_impl_->WriteImpl(write_options, GetWriteBatch()->GetWriteBatch(),
/*callback*/ nullptr, log_used, /*log ref*/
0, !DISABLE_MEMTABLE, &seq_used, prepare_batch_cnt_,
&add_prepared_callback);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
auto prepare_seq = seq_used;
// Only call SetId if it hasn't been set yet.
if (GetId() == 0) {
SetId(prepare_seq);
}
// unprep_seqs_ will also contain prepared seqnos since they are treated in
// the same way in the prepare/commit callbacks. See the comment on the
// definition of unprep_seqs_.
unprep_seqs_[prepare_seq] = prepare_batch_cnt_;
// Reset transaction state.
if (!prepared) {
prepare_batch_cnt_ = 0;
write_batch_.Clear();
WriteBatchInternal::InsertNoop(write_batch_.GetWriteBatch());
}
return s;
}
Status WriteUnpreparedTxn::PrepareInternal() {
const bool kPrepared = true;
return FlushWriteBatchToDB(kPrepared);
}
Status WriteUnpreparedTxn::CommitWithoutPrepareInternal() {
if (unprep_seqs_.empty()) {
assert(log_number_ == 0);
assert(GetId() == 0);
return WritePreparedTxn::CommitWithoutPrepareInternal();
}
// TODO(lth): We should optimize commit without prepare to not perform
// a prepare under the hood.
auto s = PrepareInternal();
if (!s.ok()) {
return s;
}
return CommitInternal();
}
Status WriteUnpreparedTxn::CommitInternal() {
// TODO(lth): Reduce duplicate code with WritePrepared commit logic.
// 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);
}
const bool includes_data = !empty && !for_recovery;
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.
WriteUnpreparedCommitEntryPreReleaseCallback update_commit_map(
wpt_db_, db_impl_, unprep_seqs_, 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.
for (const auto& seq : unprep_seqs_) {
wpt_db_->RemovePrepared(seq.first, seq.second);
}
}
unprep_seqs_.clear();
write_set_keys_.clear();
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
__attribute__((__unused__))) override {
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.
for (const auto& seq : unprep_seqs_) {
wpt_db_->RemovePrepared(seq.first, seq.second);
}
unprep_seqs_.clear();
write_set_keys_.clear();
return s;
}
Status WriteUnpreparedTxn::RollbackInternal() {
// TODO(lth): Reduce duplicate code with WritePrepared rollback logic.
WriteBatchWithIndex rollback_batch(
wpt_db_->DefaultColumnFamily()->GetComparator(), 0, true, 0);
assert(GetId() != kMaxSequenceNumber);
assert(GetId() > 0);
const auto& cf_map = *wupt_db_->GetCFHandleMap();
auto read_at_seq = kMaxSequenceNumber;
Status s;
ReadOptions roptions;
// Note that we do not use WriteUnpreparedTxnReadCallback because we do not
// need to read our own writes when reading prior versions of the key for
// rollback.
WritePreparedTxnReadCallback callback(wpt_db_, read_at_seq, 0);
for (const auto& cfkey : write_set_keys_) {
const auto cfid = cfkey.first;
const auto& keys = cfkey.second;
for (const auto& key : keys) {
const auto& cf_handle = cf_map.at(cfid);
PinnableSlice pinnable_val;
bool not_used;
s = db_impl_->GetImpl(roptions, cf_handle, key, &pinnable_val, &not_used,
&callback);
if (s.ok()) {
s = rollback_batch.Put(cf_handle, key, pinnable_val);
assert(s.ok());
} else if (s.IsNotFound()) {
s = rollback_batch.Delete(cf_handle, key);
assert(s.ok());
} else {
return s;
}
}
}
// The Rollback marker will be used as a batch separator
WriteBatchInternal::MarkRollback(rollback_batch.GetWriteBatch(), 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;
// TODO(lth): We write rollback batch all in a single batch here, but this
// should be subdivded into multiple batches as well. In phase 2, when key
// sets are read from WAL, this will happen naturally.
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_.
WriteUnpreparedCommitEntryPreReleaseCallback update_commit_map(
wpt_db_, db_impl_, unprep_seqs_, 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.GetWriteBatch(),
nullptr, nullptr, NO_REF_LOG, !DISABLE_MEMTABLE,
&seq_used, rollback_batch.SubBatchCnt(),
do_one_write ? &update_commit_map : nullptr);
assert(!s.ok() || seq_used != kMaxSequenceNumber);
if (!s.ok()) {
return s;
}
if (do_one_write) {
for (const auto& seq : unprep_seqs_) {
wpt_db_->RemovePrepared(seq.first, seq.second);
}
unprep_seqs_.clear();
write_set_keys_.clear();
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 (const auto& seq : unprep_seqs_) {
for (size_t i = 0; i < seq.second; i++) {
wpt_db_->AddCommitted(seq.first + i, rollback_seq);
}
}
for (const auto& seq : unprep_seqs_) {
wpt_db_->RemovePrepared(seq.first, seq.second);
}
}
unprep_seqs_.clear();
write_set_keys_.clear();
return s;
}
Status WriteUnpreparedTxn::Get(const ReadOptions& options,
ColumnFamilyHandle* column_family,
const Slice& key, PinnableSlice* value) {
auto snapshot = 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_;
}
WriteUnpreparedTxnReadCallback callback(wupt_db_, snap_seq, min_uncommitted,
this);
return write_batch_.GetFromBatchAndDB(db_, options, column_family, key, value,
&callback);
}
Iterator* WriteUnpreparedTxn::GetIterator(const ReadOptions& options) {
return GetIterator(options, wupt_db_->DefaultColumnFamily());
}
Iterator* WriteUnpreparedTxn::GetIterator(const ReadOptions& options,
ColumnFamilyHandle* column_family) {
// Make sure to get iterator from WriteUnprepareTxnDB, not the root db.
Iterator* db_iter = wupt_db_->NewIterator(options, column_family, this);
assert(db_iter);
return write_batch_.NewIteratorWithBase(column_family, db_iter);
}
const std::map<SequenceNumber, size_t>&
WriteUnpreparedTxn::GetUnpreparedSequenceNumbers() {
return unprep_seqs_;
}
} // namespace rocksdb
#endif // ROCKSDB_LITE