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0bd4dcde6b
Summary:
**This PR does not affect the functionality of `DB` and write-committed transactions.**
`CompactionIterator` uses `KeyCommitted(seq)` to determine if a key in the database is committed.
As the name 'write-committed' implies, if write-committed policy is used, a key exists in the database only if
it is committed. In fact, the implementation of `KeyCommitted()` is as follows:
```
inline bool KeyCommitted(SequenceNumber seq) {
// For non-txn-db and write-committed, snapshot_checker_ is always nullptr.
return snapshot_checker_ == nullptr ||
snapshot_checker_->CheckInSnapshot(seq, kMaxSequence) == SnapshotCheckerResult::kInSnapshot;
}
```
With that being said, we focus on write-prepared/write-unprepared transactions.
A few notes:
- A key can exist in the db even if it's uncommitted. Therefore, we rely on `snapshot_checker_` to determine data visibility. We also require that all writes go through transaction API instead of the raw `WriteBatch` + `Write`, thus at most one uncommitted version of one user key can exist in the database.
- `CompactionIterator` outputs a key as long as the key is uncommitted.
Due to the above reasons, it is possible that `CompactionIterator` decides to output an uncommitted key without
doing further checks on the key (`NextFromInput()`). By the time the key is being prepared for output, the key becomes
committed because the `snapshot_checker_(seq, kMaxSequence)` becomes true in the implementation of `KeyCommitted()`.
Then `CompactionIterator` will try to zero its sequence number and hit assertion error if the key is a tombstone.
To fix this issue, we should make the `CompactionIterator` see a consistent view of the input keys. Note that
for write-prepared/write-unprepared, the background flush/compaction jobs already take a "job snapshot" before starting
processing keys. The job snapshot is released only after the entire flush/compaction finishes. We can use this snapshot
to determine whether a key is committed or not with minor change to `KeyCommitted()`.
```
inline bool KeyCommitted(SequenceNumber sequence) {
// For non-txn-db and write-committed, snapshot_checker_ is always nullptr.
return snapshot_checker_ == nullptr ||
snapshot_checker_->CheckInSnapshot(sequence, job_snapshot_) ==
SnapshotCheckerResult::kInSnapshot;
}
```
As a result, whether a key is committed or not will remain a constant throughout compaction, causing no trouble
for `CompactionIterator`s assertions.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9830
Test Plan: make check
Reviewed By: ltamasi
Differential Revision: D35561162
Pulled By: riversand963
fbshipit-source-id: 0e00d200c195240341cfe6d34cbc86798b315b9f
75 lines
3 KiB
C++
75 lines
3 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include <string>
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#include <utility>
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#include <vector>
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#include "db/range_tombstone_fragmenter.h"
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#include "db/table_properties_collector.h"
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#include "logging/event_logger.h"
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#include "options/cf_options.h"
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#include "rocksdb/comparator.h"
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#include "rocksdb/env.h"
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#include "rocksdb/listener.h"
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#include "rocksdb/options.h"
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#include "rocksdb/status.h"
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#include "rocksdb/table_properties.h"
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#include "rocksdb/types.h"
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#include "table/scoped_arena_iterator.h"
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namespace ROCKSDB_NAMESPACE {
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struct FileMetaData;
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class VersionSet;
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class BlobFileAddition;
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class SnapshotChecker;
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class TableCache;
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class TableBuilder;
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class WritableFileWriter;
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class InternalStats;
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class BlobFileCompletionCallback;
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// Convenience function for NewTableBuilder on the embedded table_factory.
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TableBuilder* NewTableBuilder(const TableBuilderOptions& tboptions,
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WritableFileWriter* file);
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// Build a Table file from the contents of *iter. The generated file
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// will be named according to number specified in meta. On success, the rest of
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// *meta will be filled with metadata about the generated table.
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// If no data is present in *iter, meta->file_size will be set to
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// zero, and no Table file will be produced.
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//
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// @param column_family_name Name of the column family that is also identified
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// by column_family_id, or empty string if unknown.
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extern Status BuildTable(
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const std::string& dbname, VersionSet* versions,
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const ImmutableDBOptions& db_options, const TableBuilderOptions& tboptions,
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const FileOptions& file_options, TableCache* table_cache,
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InternalIterator* iter,
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std::vector<std::unique_ptr<FragmentedRangeTombstoneIterator>>
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range_del_iters,
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FileMetaData* meta, std::vector<BlobFileAddition>* blob_file_additions,
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std::vector<SequenceNumber> snapshots,
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SequenceNumber earliest_write_conflict_snapshot,
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SequenceNumber job_snapshot, SnapshotChecker* snapshot_checker,
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bool paranoid_file_checks, InternalStats* internal_stats,
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IOStatus* io_status, const std::shared_ptr<IOTracer>& io_tracer,
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BlobFileCreationReason blob_creation_reason,
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EventLogger* event_logger = nullptr, int job_id = 0,
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const Env::IOPriority io_priority = Env::IO_HIGH,
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TableProperties* table_properties = nullptr,
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Env::WriteLifeTimeHint write_hint = Env::WLTH_NOT_SET,
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const std::string* full_history_ts_low = nullptr,
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BlobFileCompletionCallback* blob_callback = nullptr,
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uint64_t* num_input_entries = nullptr,
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uint64_t* memtable_payload_bytes = nullptr,
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uint64_t* memtable_garbage_bytes = nullptr);
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} // namespace ROCKSDB_NAMESPACE
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