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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <queue>
#include <tuple>
#include "mongo/db/namespace_string.h"
#include "mongo/db/repl/oplog_buffer.h"
#include "mongo/platform/mutex.h"
#include "mongo/util/queue.h"
namespace mongo {
namespace repl {
class StorageInterface;
/**
* Oplog buffer backed by a temporary collection. This collection is created in startup() and
* removed in shutdown(). The documents will be popped and peeked in timestamp order.
*/
class OplogBufferCollection : public OplogBuffer {
public:
/**
* Structure used to configure an instance of OplogBufferCollection.
*/
struct Options {
// If equal to 0, the cache size will be set to 1.
std::size_t peekCacheSize = 0;
bool dropCollectionAtStartup = true;
bool dropCollectionAtShutdown = true;
Options() {}
};
/**
* Returns default namespace for temporary collection used to hold data in oplog buffer.
*/
static NamespaceString getDefaultNamespace();
/**
* Returns the embedded document in the 'entry' field.
*/
static BSONObj extractEmbeddedOplogDocument(const BSONObj& orig);
/**
* Creates and returns a document suitable for storing in the collection together with the
* associated timestamp and sentinel count that determines the position of this document in the
* _id index.
*
* If 'orig' is a valid oplog entry, the '_id' field of the returned BSONObj will be:
* {
* ts: 'ts' field of the provided document,
* s: 0
* }
* The timestamp returned will be equal to as the 'ts' field in the BSONObj.
* Assumes there is a 'ts' field in the original document.
*
* If 'orig' is an empty document (ie. we're inserting a sentinel value), the '_id' field will
* be generated based on the timestamp of the last document processed and the total number of
* sentinels with the same timestamp (including the document about to be inserted. For example,
* the first sentinel to be inserted after a valid oplog entry will have the following '_id'
* field:
* {
* ts: 'ts' field of the last inserted valid oplog entry,
* s: 1
* }
* The sentinel counter will be reset to 0 on inserting the next valid oplog entry.
*/
static std::tuple<BSONObj, Timestamp, std::size_t> addIdToDocument(
const BSONObj& orig, const Timestamp& lastTimestamp, std::size_t sentinelCount);
explicit OplogBufferCollection(StorageInterface* storageInterface, Options options = Options());
OplogBufferCollection(StorageInterface* storageInterface,
const NamespaceString& nss,
Options options = Options());
/**
* Returns the namespace string of the collection used by this oplog buffer.
*/
NamespaceString getNamespace() const;
/**
* Returns the options used to configure this OplogBufferCollection
*/
Options getOptions() const;
void startup(OperationContext* opCtx) override;
void shutdown(OperationContext* opCtx) override;
void push(OperationContext* opCtx,
Batch::const_iterator begin,
Batch::const_iterator end) override;
void waitForSpace(OperationContext* opCtx, std::size_t size) override;
bool isEmpty() const override;
std::size_t getMaxSize() const override;
std::size_t getSize() const override;
std::size_t getCount() const override;
void clear(OperationContext* opCtx) override;
bool tryPop(OperationContext* opCtx, Value* value) override;
bool waitForData(Seconds waitDuration) override;
bool peek(OperationContext* opCtx, Value* value) override;
boost::optional<Value> lastObjectPushed(OperationContext* opCtx) const override;
// ---- Testing API ----
std::size_t getSentinelCount_forTest() const;
Timestamp getLastPushedTimestamp_forTest() const;
Timestamp getLastPoppedTimestamp_forTest() const;
std::queue<BSONObj> getPeekCache_forTest() const;
private:
/*
* Creates a temporary collection with the _nss namespace.
*/
void _createCollection(OperationContext* opCtx);
/*
* Drops the collection with the _nss namespace.
*/
void _dropCollection(OperationContext* opCtx);
enum class PeekMode { kExtractEmbeddedDocument, kReturnUnmodifiedDocumentFromCollection };
/**
* Returns the oldest oplog entry in the buffer.
* Assumes the buffer is not empty.
*/
BSONObj _peek_inlock(OperationContext* opCtx, PeekMode peekMode);
// Storage interface used to perform storage engine level functions on the collection.
StorageInterface* _storageInterface;
/**
* Pops an entry off the buffer in a lock.
*/
bool _pop_inlock(OperationContext* opCtx, Value* value);
/**
* Returns the last document pushed onto the collection. This does not remove the `_id` field
* of the document. If the collection is empty, this returns boost::none.
*/
boost::optional<Value> _lastDocumentPushed_inlock(OperationContext* opCtx) const;
// The namespace for the oplog buffer collection.
const NamespaceString _nss;
// These are the options with which the oplog buffer was configured at construction time.
const Options _options;
// Allows functions to wait until the queue has data. This condition variable is used with
// _mutex below.
stdx::condition_variable _cvNoLongerEmpty;
// Protects member data below and synchronizes it with the underlying collection.
mutable Mutex _mutex = MONGO_MAKE_LATCH("OplogBufferCollection::_mutex");
// Number of documents in buffer.
std::size_t _count = 0;
// Size of documents in buffer.
std::size_t _size = 0;
// Number of sentinel values inserted so far with the same timestamp as '_lastPoppedKey'.
std::size_t _sentinelCount = 0;
Timestamp _lastPushedTimestamp;
BSONObj _lastPoppedKey;
// Used by _peek_inlock() to hold results of the read ahead query that will be used for pop/peek
// results.
std::queue<BSONObj> _peekCache;
};
} // namespace repl
} // namespace mongo
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