rocksdb/db/snapshot.h
Igor Canadi 6c6037f60c Expose Snapshot's SequenceNumber
Summary:
Requested here: https://www.facebook.com/groups/rocksdb.dev/permalink/705524519546065/

It might also help with mongo. I don't see a reason why we shouldn't expose this info.

Test Plan: make check

Reviewers: sdong, yhchiang, rven

Reviewed By: rven

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D32547
2015-01-29 18:22:43 -08:00

106 lines
2.7 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.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include "rocksdb/db.h"
namespace rocksdb {
class SnapshotList;
// Snapshots are kept in a doubly-linked list in the DB.
// Each SnapshotImpl corresponds to a particular sequence number.
class SnapshotImpl : public Snapshot {
public:
SequenceNumber number_; // const after creation
virtual SequenceNumber GetSequenceNumber() const { return number_; }
private:
friend class SnapshotList;
// SnapshotImpl is kept in a doubly-linked circular list
SnapshotImpl* prev_;
SnapshotImpl* next_;
SnapshotList* list_; // just for sanity checks
int64_t unix_time_;
};
class SnapshotList {
public:
SnapshotList() {
list_.prev_ = &list_;
list_.next_ = &list_;
list_.number_ = 0xFFFFFFFFL; // placeholder marker, for debugging
count_ = 0;
}
bool empty() const { return list_.next_ == &list_; }
SnapshotImpl* oldest() const { assert(!empty()); return list_.next_; }
SnapshotImpl* newest() const { assert(!empty()); return list_.prev_; }
const SnapshotImpl* New(SequenceNumber seq, uint64_t unix_time) {
SnapshotImpl* s = new SnapshotImpl;
s->number_ = seq;
s->unix_time_ = unix_time;
s->list_ = this;
s->next_ = &list_;
s->prev_ = list_.prev_;
s->prev_->next_ = s;
s->next_->prev_ = s;
count_++;
return s;
}
void Delete(const SnapshotImpl* s) {
assert(s->list_ == this);
s->prev_->next_ = s->next_;
s->next_->prev_ = s->prev_;
count_--;
delete s;
}
// retrieve all snapshot numbers. They are sorted in ascending order.
void getAll(std::vector<SequenceNumber>& ret) {
if (empty()) return;
SnapshotImpl* s = &list_;
while (s->next_ != &list_) {
ret.push_back(s->next_->number_);
s = s ->next_;
}
}
// get the sequence number of the most recent snapshot
SequenceNumber GetNewest() {
if (empty()) {
return 0;
}
return newest()->number_;
}
int64_t GetOldestSnapshotTime() const {
if (empty()) {
return 0;
} else {
return oldest()->unix_time_;
}
}
uint64_t count() const { return count_; }
private:
// Dummy head of doubly-linked list of snapshots
SnapshotImpl list_;
uint64_t count_;
};
} // namespace rocksdb