rocksdb/db/tailing_iter.h
Yueh-Hsuan Chiang 118f88d25d Fix compile error in tailing_iter.h
Summary:
Fix the following compile error

  ./db/tailing_iter.h:17:1: error: class 'SuperVersion' was previously declared as a struct [-Werror,-Wmismatched-tags]
  class SuperVersion;
  ^
  ./db/column_family.h:77:8: note: previous use is here
  struct SuperVersion {
         ^
         ./db/tailing_iter.h:17:1: note: did you mean struct here?
         class SuperVersion;
         ^~~~~
         struct
         1 error generated.

Test Plan: make

Reviewers: ljin, igor, haobo, sdong

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17799
2014-04-14 14:05:15 -07:00

95 lines
2.9 KiB
C++

// 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;
class Env;
struct SuperVersion;
class ColumnFamilyData;
/**
* 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(Env* const env, DBImpl* db, const ReadOptions& read_options,
ColumnFamilyData* cfd);
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:
void Cleanup();
Env* const env_;
DBImpl* const db_;
const ReadOptions read_options_;
ColumnFamilyData* const cfd_;
SuperVersion* super_version_;
// 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