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rocksdb/db/tailing_iter.h

88 lines
2.8 KiB

// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#pragma once
#include <string>
#include "rocksdb/db.h"
#include "rocksdb/iterator.h"
#include "rocksdb/options.h"
namespace rocksdb {
class DBImpl;
/**
* TailingIterator is a special type of iterator that doesn't use an (implicit)
* snapshot. In other words, it can be used to read data that was added to the
* db after the iterator had been created.
*
* TailingIterator is optimized for sequential reading. It doesn't support
* Prev() and SeekToLast() operations.
*/
class TailingIterator : public Iterator {
public:
TailingIterator(DBImpl* db, const ReadOptions& options,
const Comparator* comparator);
virtual ~TailingIterator() {}
virtual bool Valid() const override;
virtual void SeekToFirst() override;
virtual void SeekToLast() override;
virtual void Seek(const Slice& target) override;
virtual void Next() override;
virtual void Prev() override;
virtual Slice key() const override;
virtual Slice value() const override;
virtual Status status() const override;
private:
DBImpl* const db_;
const ReadOptions options_;
const Comparator* const comparator_;
uint64_t version_number_;
// TailingIterator merges the contents of the two iterators below (one using
// mutable memtable contents only, other over SSTs and immutable memtables).
// See DBIter::GetTailingIteratorPair().
std::unique_ptr<Iterator> mutable_;
std::unique_ptr<Iterator> immutable_;
// points to either mutable_ or immutable_
Iterator* current_;
// key that precedes immutable iterator's current key
std::string prev_key_;
// unless prev_set is true, prev_key/prev_head is not valid and shouldn't be
// used; reset by createIterators()
bool is_prev_set_;
// prev_key_ was set by SeekImmutable(), which means that the interval of
// keys covered by immutable_ is [prev_key_, current], i.e. it includes the
// left endpoint
bool is_prev_inclusive_;
// internal iterator status
Status status_;
// check if this iterator's version matches DB's version
bool IsCurrentVersion() const;
// check if SeekImmutable() is needed due to target having a different prefix
// than prev_key_ (used when options.prefix_seek is set)
bool IsSamePrefix(const Slice& target) const;
// creates mutable_ and immutable_ iterators and updates version_number_
void CreateIterators();
// set current_ to be one of the iterators with the smallest key
void UpdateCurrent();
// seek on immutable_ and update prev_key
void SeekImmutable(const Slice& target);
};
} // namespace rocksdb