fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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88 lines
2.8 KiB
88 lines
2.8 KiB
// 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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#include <string>
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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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namespace rocksdb {
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class DBImpl;
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/**
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* TailingIterator is a special type of iterator that doesn't use an (implicit)
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* snapshot. In other words, it can be used to read data that was added to the
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* db after the iterator had been created.
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*
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* TailingIterator is optimized for sequential reading. It doesn't support
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* Prev() and SeekToLast() operations.
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*/
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class TailingIterator : public Iterator {
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public:
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TailingIterator(DBImpl* db, const ReadOptions& options,
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const Comparator* comparator);
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virtual ~TailingIterator() {}
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virtual bool Valid() const override;
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virtual void SeekToFirst() override;
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virtual void SeekToLast() 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 void Prev() 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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DBImpl* const db_;
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const ReadOptions options_;
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const Comparator* const comparator_;
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uint64_t version_number_;
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// TailingIterator merges the contents of the two iterators below (one using
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// mutable memtable contents only, other over SSTs and immutable memtables).
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// See DBIter::GetTailingIteratorPair().
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std::unique_ptr<Iterator> mutable_;
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std::unique_ptr<Iterator> immutable_;
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// points to either mutable_ or immutable_
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Iterator* current_;
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// key that precedes immutable iterator's current key
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std::string prev_key_;
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// unless prev_set is true, prev_key/prev_head is not valid and shouldn't be
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// used; reset by createIterators()
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bool is_prev_set_;
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// prev_key_ was set by SeekImmutable(), which means that the interval of
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// keys covered by immutable_ is [prev_key_, current], i.e. it includes the
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// left endpoint
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bool is_prev_inclusive_;
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// internal iterator status
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Status status_;
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// check if this iterator's version matches DB's version
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bool IsCurrentVersion() const;
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// check if SeekImmutable() is needed due to target having a different prefix
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// than prev_key_ (used when options.prefix_seek is set)
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bool IsSamePrefix(const Slice& target) const;
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// creates mutable_ and immutable_ iterators and updates version_number_
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void CreateIterators();
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// set current_ to be one of the iterators with the smallest key
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void UpdateCurrent();
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// seek on immutable_ and update prev_key
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void SeekImmutable(const Slice& target);
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};
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} // namespace rocksdb
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