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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 <string>
#include <wiredtiger.h>
#include "mongo/base/string_data.h"
#include "mongo/db/storage/wiredtiger/wiredtiger_session_cache.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/platform/mutex.h"
#include "mongo/util/string_map.h"
namespace mongo {
/**
* The WiredTigerSizeStorer class serves as a write buffer to durably store size information for
* MongoDB collections. The size storer uses a separate WiredTiger table as key-value store, where
* the URI serves as key and the value is a BSON document with `numRecords` and `dataSize` fields.
* This buffering is neccessary to allow concurrent updates of size information without causing
* write conflicts. The dirty size information is periodically stored written back to the table,
* including on clean shutdown and/or catalog reload. Crashes or replica-set fail-overs may result
* in size updates to be lost, so size information is only approximate. Reads use the buffer for
* pending stores, or otherwise read directly from the WiredTiger table using a dedicated session
* and cursor.
*/
class WiredTigerSizeStorer {
public:
/**
* SizeInfo is a thread-safe buffer for keeping track of the number of documents in a collection
* and their data size. Storing a SizeInfo in the WiredTigerSizeStorer results in shared
* ownership. The SizeInfo may still be updated after it is stored in the SizeStorer.
* The 'dirty' field is used by the size storer to cheaply merge duplicate stores of the same
* SizeInfo.
*/
struct SizeInfo {
SizeInfo() = default;
SizeInfo(long long records, long long size) : numRecords(records), dataSize(size) {}
~SizeInfo() {
invariant(!_dirty.load());
}
AtomicWord<long long> numRecords;
AtomicWord<long long> dataSize;
private:
friend WiredTigerSizeStorer;
AtomicWord<bool> _dirty;
};
WiredTigerSizeStorer(WT_CONNECTION* conn, const std::string& storageUri);
~WiredTigerSizeStorer() = default;
/**
* Ensure that the shared SizeInfo will be stored by the next call to flush.
* Values stored are no older than the values at time of this call, but may be newer.
*/
void store(StringData uri, std::shared_ptr<SizeInfo> sizeInfo);
std::shared_ptr<SizeInfo> load(OperationContext* opCtx, StringData uri) const;
/**
* Writes all changes to the underlying table.
*/
void flush(bool syncToDisk);
private:
WT_CONNECTION* _conn;
const std::string _storageUri;
const uint64_t _tableId; // Not persisted
// Serializes flushes to disk.
Mutex _flushMutex = MONGO_MAKE_LATCH("WiredTigerSessionStorer::_flushMutex");
using Buffer = StringMap<std::shared_ptr<SizeInfo>>;
mutable Mutex _bufferMutex =
MONGO_MAKE_LATCH("WiredTigerSessionStorer::_bufferMutex"); // Guards _buffer
Buffer _buffer;
};
} // namespace mongo
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