rocksdb/utilities/transactions/transaction_util.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
#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/string_util.h"
namespace rocksdb {
Status TransactionUtil::CheckKeyForConflicts(
DBImpl* db_impl, ColumnFamilyHandle* column_family, const std::string& key,
SequenceNumber snap_seq, bool cache_only, ReadCallback* snap_checker,
SequenceNumber min_uncommitted) {
Status result;
auto cfh = reinterpret_cast<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, 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, 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: ",
ToString(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 "
Refactor trimming logic for immutable memtables (#5022) Summary: MyRocks currently sets `max_write_buffer_number_to_maintain` in order to maintain enough history for transaction conflict checking. The effectiveness of this approach depends on the size of memtables. When memtables are small, it may not keep enough history; when memtables are large, this may consume too much memory. We are proposing a new way to configure memtable list history: by limiting the memory usage of immutable memtables. The new option is `max_write_buffer_size_to_maintain` and it will take precedence over the old `max_write_buffer_number_to_maintain` if they are both set to non-zero values. The new option accounts for the total memory usage of flushed immutable memtables and mutable memtable. When the total usage exceeds the limit, RocksDB may start dropping immutable memtables (which is also called trimming history), starting from the oldest one. The semantics of the old option actually works both as an upper bound and lower bound. History trimming will start if number of immutable memtables exceeds the limit, but it will never go below (limit-1) due to history trimming. In order the mimic the behavior with the new option, history trimming will stop if dropping the next immutable memtable causes the total memory usage go below the size limit. For example, assuming the size limit is set to 64MB, and there are 3 immutable memtables with sizes of 20, 30, 30. Although the total memory usage is 80MB > 64MB, dropping the oldest memtable will reduce the memory usage to 60MB < 64MB, so in this case no memtable will be dropped. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5022 Differential Revision: D14394062 Pulled By: miasantreble fbshipit-source-id: 60457a509c6af89d0993f988c9b5c2aa9e45f5c5
2019-08-23 22:54:09 +02:00
"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;
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,
&found_record_for_key);
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);
if (write_conflict) {
result = Status::Busy();
}
}
}
return result;
}
Status TransactionUtil::CheckKeysForConflicts(DBImpl* db_impl,
const TransactionKeyMap& key_map,
bool cache_only) {
Status result;
for (auto& key_map_iter : key_map) {
uint32_t cf_id = key_map_iter.first;
const auto& keys = key_map_iter.second;
SuperVersion* sv = db_impl->GetAndRefSuperVersion(cf_id);
if (sv == nullptr) {
result = Status::InvalidArgument("Could not access column family " +
ToString(cf_id));
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.
for (const auto& key_iter : keys) {
const auto& key = key_iter.first;
const SequenceNumber key_seq = key_iter.second.seq;
result = CheckKey(db_impl, sv, earliest_seq, key_seq, key, cache_only);
if (!result.ok()) {
break;
}
}
db_impl->ReturnAndCleanupSuperVersion(cf_id, sv);
if (!result.ok()) {
break;
}
}
return result;
}
} // namespace rocksdb
#endif // ROCKSDB_LITE