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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.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kStorage
#include "mongo/platform/basic.h"
#include "mongo/db/snapshot_window_util.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/service_context.h"
#include "mongo/db/snapshot_window_options.h"
#include "mongo/db/storage/storage_engine.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/concurrency/with_lock.h"
#include "mongo/util/fail_point_service.h"
#include "mongo/util/log.h"
namespace mongo {
// This failpoint is used for performance testing.
MONGO_FAIL_POINT_DEFINE(preventDynamicSnapshotHistoryWindowTargetAdjustments);
namespace SnapshotWindowUtil {
// Adds concurrency control to increaseTargetSnapshotWindowSize() and
// decreaseTargetSnapshotWindowSize(). They should not run concurrently with themselves or one
// another, since they act on and modify the same storage parameters. Further guards the static
// variables "_snapshotWindowLastDecreasedAt" and "_snapshotWindowLastIncreasedAt" used in
// increaseTargetSnapshotWindowSize() and decreaseSnapshowWindow().
stdx::mutex snapshotWindowMutex;
namespace {
void _decreaseTargetSnapshotWindowSize(WithLock lock, OperationContext* opCtx) {
// Tracks the last time that the snapshot window was decreased so that it does not go down so
// fast that the system does not have time to react and reduce snapshot availability.
static Date_t _snapshotWindowLastDecreasedAt{Date_t::min()};
if (_snapshotWindowLastDecreasedAt >
(Date_t::now() -
Milliseconds(snapshotWindowParams.minMillisBetweenSnapshotWindowDec.load()))) {
// We have already decreased the window size in the last minMillisBetweenSnapshotWindowDec
// milliseconds.
return;
}
snapshotWindowParams.targetSnapshotHistoryWindowInSeconds.store(
snapshotWindowParams.targetSnapshotHistoryWindowInSeconds.load() *
snapshotWindowParams.snapshotWindowMultiplicativeDecrease.load());
// Try to set the oldest_timestamp immediately without waiting for a write to adjust the
// window. May or may not work depending on the state of the system.
StorageEngine* engine = opCtx->getServiceContext()->getStorageEngine();
invariant(engine);
engine->setOldestTimestampFromStable();
_snapshotWindowLastDecreasedAt = Date_t::now();
}
} // namespace
void increaseTargetSnapshotWindowSize(OperationContext* opCtx) {
if (MONGO_FAIL_POINT(preventDynamicSnapshotHistoryWindowTargetAdjustments)) {
return;
}
stdx::unique_lock<stdx::mutex> lock(snapshotWindowMutex);
// Tracks the last time that the snapshot window was increased so that it does not go up so fast
// that the storage engine does not have time to improve snapshot availability.
static Date_t _snapshotWindowLastIncreasedAt{Date_t::min()};
if (_snapshotWindowLastIncreasedAt >
(Date_t::now() -
Milliseconds(snapshotWindowParams.minMillisBetweenSnapshotWindowInc.load()))) {
// We have already increased the window size in the last minMillisBetweenSnapshotWindowInc
// milliseconds.
return;
}
// If the cache pressure is already too high, we will not put more pressure on it by increasing
// the window size.
StorageEngine* engine = opCtx->getServiceContext()->getStorageEngine();
if (engine && engine->isCacheUnderPressure(opCtx)) {
warning() << "Attempted to increase the time window of available snapshots for "
"point-in-time operations (readConcern level 'snapshot' or transactions), but "
"the storage engine cache pressure, per the cachePressureThreshold setting of "
"'"
<< snapshotWindowParams.cachePressureThreshold.load()
<< "', is too high to allow it to increase. If this happens frequently, consider "
"either increasing the cache pressure threshold or increasing the memory "
"available to the storage engine cache, in order to improve the success rate "
"or speed of point-in-time requests.";
_decreaseTargetSnapshotWindowSize(lock, opCtx);
return;
}
if (snapshotWindowParams.targetSnapshotHistoryWindowInSeconds.load() ==
snapshotWindowParams.maxTargetSnapshotHistoryWindowInSeconds.load()) {
warning() << "Attempted to increase the time window of available snapshots for "
"point-in-time operations (readConcern level 'snapshot' or transactions), but "
"maxTargetSnapshotHistoryWindowInSeconds has already been reached. If this "
"happens frequently, consider increasing the "
"maxTargetSnapshotHistoryWindowInSeconds setting value, which is currently "
"set to '"
<< snapshotWindowParams.maxTargetSnapshotHistoryWindowInSeconds.load() << "'.";
return;
}
int increasedSnapshotWindow = snapshotWindowParams.targetSnapshotHistoryWindowInSeconds.load() +
snapshotWindowParams.snapshotWindowAdditiveIncreaseSeconds.load();
snapshotWindowParams.targetSnapshotHistoryWindowInSeconds.store(
std::min(increasedSnapshotWindow,
snapshotWindowParams.maxTargetSnapshotHistoryWindowInSeconds.load()));
_snapshotWindowLastIncreasedAt = Date_t::now();
}
void decreaseTargetSnapshotWindowSize(OperationContext* opCtx) {
if (MONGO_FAIL_POINT(preventDynamicSnapshotHistoryWindowTargetAdjustments)) {
return;
}
stdx::unique_lock<stdx::mutex> lock(snapshotWindowMutex);
StorageEngine* engine = opCtx->getServiceContext()->getStorageEngine();
if (engine && engine->isCacheUnderPressure(opCtx)) {
_decreaseTargetSnapshotWindowSize(lock, opCtx);
}
}
} // namespace SnapshotWindowUtil
} // namespace mongo
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