187b29938c
Summary: Since ForwardIterator is on a level below DBIter, the latter may call Next() on it (e.g. in order to skip deletion markers). Since this also updates `prev_key_`, it may prevent the Seek() optimization. For example, assume that there's only one SST file and it contains the following entries: 0101, 0201 (`ValueType::kTypeDeletion`, i.e. a tombstone record), 0201 (`kTypeValue`), 0202. Memtable is empty. `Seek(0102)` will result in `prev_key_` being set to `0201` instead of `0102`, since `DBIter::Seek()` will call `ForwardIterator::Next()` to skip record 0201. Therefore, when `Seek(0102)` is called again, `NeedToSeekImmutable()` will return true. This fix relies on `prefix_extractor_` to detect prefix changes. `prev_key_` is only set to `current_->key()` as long as they have the same prefix. I also made a small change to `NeedToSeekImmutable()` so it no longer returns true when the db is empty (i.e. there's nothing but a memtable). Test Plan: $ TEST_TMPDIR=/dev/shm/rocksdbtest ROCKSDB_TESTS=TailingIterator ./db_test Reviewers: sdong, igor, ljin Reviewed By: ljin Subscribers: leveldb Differential Revision: https://reviews.facebook.net/D23823
110 lines
3.0 KiB
C++
110 lines
3.0 KiB
C++
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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#pragma once
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#ifndef ROCKSDB_LITE
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#include <string>
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#include <vector>
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#include <queue>
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#include "rocksdb/db.h"
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#include "rocksdb/iterator.h"
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#include "rocksdb/options.h"
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#include "db/dbformat.h"
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#include "util/arena.h"
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namespace rocksdb {
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class DBImpl;
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class Env;
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struct SuperVersion;
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class ColumnFamilyData;
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class LevelIterator;
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struct FileMetaData;
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class MinIterComparator {
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public:
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explicit MinIterComparator(const Comparator* comparator) :
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comparator_(comparator) {}
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bool operator()(Iterator* a, Iterator* b) {
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return comparator_->Compare(a->key(), b->key()) > 0;
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}
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private:
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const Comparator* comparator_;
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};
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typedef std::priority_queue<Iterator*,
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std::vector<Iterator*>,
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MinIterComparator> MinIterHeap;
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/**
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* ForwardIterator is a special type of iterator that only supports Seek()
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* and Next(). It is expected to perform better than TailingIterator by
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* removing the encapsulation and making all information accessible within
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* the iterator. At the current implementation, snapshot is taken at the
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* time Seek() is called. The Next() followed do not see new values after.
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*/
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class ForwardIterator : public Iterator {
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public:
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ForwardIterator(DBImpl* db, const ReadOptions& read_options,
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ColumnFamilyData* cfd);
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virtual ~ForwardIterator();
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void SeekToLast() override {
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status_ = Status::NotSupported("ForwardIterator::SeekToLast()");
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valid_ = false;
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}
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void Prev() {
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status_ = Status::NotSupported("ForwardIterator::Prev");
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valid_ = false;
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}
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virtual bool Valid() const override;
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void SeekToFirst() override;
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virtual void Seek(const Slice& target) override;
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virtual void Next() override;
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virtual Slice key() const override;
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virtual Slice value() const override;
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virtual Status status() const override;
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private:
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void Cleanup();
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void RebuildIterators();
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void ResetIncompleteIterators();
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void SeekInternal(const Slice& internal_key, bool seek_to_first);
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void UpdateCurrent();
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bool NeedToSeekImmutable(const Slice& internal_key);
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uint32_t FindFileInRange(
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const std::vector<FileMetaData*>& files, const Slice& internal_key,
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uint32_t left, uint32_t right);
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DBImpl* const db_;
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const ReadOptions read_options_;
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ColumnFamilyData* const cfd_;
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const SliceTransform* const prefix_extractor_;
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const Comparator* user_comparator_;
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MinIterHeap immutable_min_heap_;
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SuperVersion* sv_;
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Iterator* mutable_iter_;
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std::vector<Iterator*> imm_iters_;
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std::vector<Iterator*> l0_iters_;
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std::vector<LevelIterator*> level_iters_;
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Iterator* current_;
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// internal iterator status
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Status status_;
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bool valid_;
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IterKey prev_key_;
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bool is_prev_set_;
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bool is_prev_inclusive_;
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Arena arena_;
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};
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} // namespace rocksdb
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#endif // ROCKSDB_LITE
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