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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
#include "utilities/transactions/transaction_util.h"
#include <cinttypes>
#include <string>
#include <vector>
#include "db/db_impl/db_impl.h"
#include "rocksdb/status.h"
#include "rocksdb/utilities/write_batch_with_index.h"
#include "util/cast_util.h"
#include "util/string_util.h"
namespace ROCKSDB_NAMESPACE {
Status TransactionUtil::CheckKeyForConflicts(
DBImpl* db_impl, ColumnFamilyHandle* column_family, const std::string& key,
SequenceNumber snap_seq, const std::string* const read_ts, bool cache_only,
ReadCallback* snap_checker, SequenceNumber min_uncommitted) {
Status result;
auto cfh = static_cast_with_check<ColumnFamilyHandleImpl>(column_family);
auto cfd = cfh->cfd();
SuperVersion* sv = db_impl->GetAndRefSuperVersion(cfd);
if (sv == nullptr) {
result = Status::InvalidArgument("Could not access column family " +
cfh->GetName());
}
if (result.ok()) {
SequenceNumber earliest_seq =
db_impl->GetEarliestMemTableSequenceNumber(sv, true);
result = CheckKey(db_impl, sv, earliest_seq, snap_seq, key, read_ts,
cache_only, snap_checker, min_uncommitted);
db_impl->ReturnAndCleanupSuperVersion(cfd, sv);
}
return result;
}
Status TransactionUtil::CheckKey(DBImpl* db_impl, SuperVersion* sv,
SequenceNumber earliest_seq,
SequenceNumber snap_seq,
const std::string& key,
const std::string* const read_ts,
bool cache_only, ReadCallback* snap_checker,
SequenceNumber min_uncommitted) {
// When `min_uncommitted` is provided, keys are not always committed
// in sequence number order, and `snap_checker` is used to check whether
// specific sequence number is in the database is visible to the transaction.
// So `snap_checker` must be provided.
assert(min_uncommitted == kMaxSequenceNumber || snap_checker != nullptr);
Status result;
bool need_to_read_sst = false;
// Since it would be too slow to check the SST files, we will only use
// the memtables to check whether there have been any recent writes
// to this key after it was accessed in this transaction. But if the
// Memtables do not contain a long enough history, we must fail the
// transaction.
if (earliest_seq == kMaxSequenceNumber) {
// The age of this memtable is unknown. Cannot rely on it to check
// for recent writes. This error shouldn't happen often in practice as
// the Memtable should have a valid earliest sequence number except in some
// corner cases (such as error cases during recovery).
need_to_read_sst = true;
if (cache_only) {
result = Status::TryAgain(
"Transaction could not check for conflicts as the MemTable does not "
"contain a long enough history to check write at SequenceNumber: ",
std::to_string(snap_seq));
}
} else if (snap_seq < earliest_seq || min_uncommitted <= earliest_seq) {
// Use <= for min_uncommitted since earliest_seq is actually the largest sec
// before this memtable was created
need_to_read_sst = true;
if (cache_only) {
// The age of this memtable is too new to use to check for recent
// writes.
char msg[300];
snprintf(msg, sizeof(msg),
"Transaction could not check for conflicts for operation at "
"SequenceNumber %" PRIu64
" as the MemTable only contains changes newer than "
"SequenceNumber %" PRIu64
". Increasing the value of the "
"max_write_buffer_size_to_maintain option could reduce the "
"frequency "
"of this error.",
snap_seq, earliest_seq);
result = Status::TryAgain(msg);
}
}
if (result.ok()) {
SequenceNumber seq = kMaxSequenceNumber;
std::string timestamp;
bool found_record_for_key = false;
// When min_uncommitted == kMaxSequenceNumber, writes are committed in
// sequence number order, so only keys larger than `snap_seq` can cause
// conflict.
// When min_uncommitted != kMaxSequenceNumber, keys lower than
// min_uncommitted will not triggered conflicts, while keys larger than
// min_uncommitted might create conflicts, so we need to read them out
// from the DB, and call callback to snap_checker to determine. So only
// keys lower than min_uncommitted can be skipped.
SequenceNumber lower_bound_seq =
(min_uncommitted == kMaxSequenceNumber) ? snap_seq : min_uncommitted;
Status s = db_impl->GetLatestSequenceForKey(
sv, key, !need_to_read_sst, lower_bound_seq, &seq,
!read_ts ? nullptr : ×tamp, &found_record_for_key,
/*is_blob_index=*/nullptr);
if (!(s.ok() || s.IsNotFound() || s.IsMergeInProgress())) {
result = s;
} else if (found_record_for_key) {
bool write_conflict = snap_checker == nullptr
? snap_seq < seq
: !snap_checker->IsVisible(seq);
// Perform conflict checking based on timestamp if applicable.
if (!write_conflict && read_ts != nullptr) {
ColumnFamilyData* cfd = sv->cfd;
assert(cfd);
const Comparator* const ucmp = cfd->user_comparator();
assert(ucmp);
assert(read_ts->size() == ucmp->timestamp_size());
assert(read_ts->size() == timestamp.size());
// Write conflict if *ts < timestamp.
write_conflict = ucmp->CompareTimestamp(*read_ts, timestamp) < 0;
}
if (write_conflict) {
result = Status::Busy();
}
}
}
return result;
}
Status TransactionUtil::CheckKeysForConflicts(DBImpl* db_impl,
const LockTracker& tracker,
bool cache_only) {
Status result;
std::unique_ptr<LockTracker::ColumnFamilyIterator> cf_it(
tracker.GetColumnFamilyIterator());
assert(cf_it != nullptr);
while (cf_it->HasNext()) {
ColumnFamilyId cf = cf_it->Next();
SuperVersion* sv = db_impl->GetAndRefSuperVersion(cf);
if (sv == nullptr) {
result = Status::InvalidArgument("Could not access column family " +
std::to_string(cf));
break;
}
SequenceNumber earliest_seq =
db_impl->GetEarliestMemTableSequenceNumber(sv, true);
// For each of the keys in this transaction, check to see if someone has
// written to this key since the start of the transaction.
std::unique_ptr<LockTracker::KeyIterator> key_it(
tracker.GetKeyIterator(cf));
assert(key_it != nullptr);
while (key_it->HasNext()) {
const std::string& key = key_it->Next();
PointLockStatus status = tracker.GetPointLockStatus(cf, key);
const SequenceNumber key_seq = status.seq;
// TODO: support timestamp-based conflict checking.
// CheckKeysForConflicts() is currently used only by optimistic
// transactions.
result = CheckKey(db_impl, sv, earliest_seq, key_seq, key,
/*read_ts=*/nullptr, cache_only);
if (!result.ok()) {
break;
}
}
db_impl->ReturnAndCleanupSuperVersion(cf, sv);
if (!result.ok()) {
break;
}
}
return result;
}
} // namespace ROCKSDB_NAMESPACE
#endif // ROCKSDB_LITE
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