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/**
* Copyright (C) 2022-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 "mongo/db/operation_context.h"
#include "mongo/db/service_context.h"
#include "mongo/s/analyze_shard_key_server_parameters_gen.h"
#include "mongo/util/periodic_runner.h"
namespace mongo {
namespace analyze_shard_key {
/**
* Owns the machinery for sampling queries on a sampler. That consists of the following:
* - The periodic background job that refreshes the last exponential moving average of the number of
* queries that this sampler executes per second.
* - The periodic background job that sends the calculated average to the coordinator to refresh the
* latest configurations. The average determines the share of the cluster-wide sample rate that
* will be assigned to this sampler.
* - The rate limiters that each controls the rate at which queries against a collection are sampled
* on this sampler.
*
* Currently, query sampling is only supported on a sharded cluster. So a sampler must be a mongos
* and the coordinator must be the config server's primary mongod.
*/
class QueryAnalysisSampler final {
QueryAnalysisSampler(const QueryAnalysisSampler&) = delete;
QueryAnalysisSampler& operator=(const QueryAnalysisSampler&) = delete;
public:
/**
* Stores the last total number of queries that this sampler has executed and the last
* exponential moving average number of queries that this sampler executes per second. The
* average is recalculated every second when the total number of queries is refreshed.
*/
struct QueryStats {
QueryStats() = default;
long long getLastTotalCount() const {
return _lastTotalCount;
}
boost::optional<double> getLastAvgCount() const {
return _lastAvgCount;
}
/**
* Refreshes the last total count and the last exponential moving average count. To be
* invoked every second.
*/
void refreshTotalCount(long long newTotalCount);
private:
double _calculateExponentialMovingAverage(double prevAvg, long long newVal) const;
const double _smoothingFactor = gQueryAnalysisQueryStatsSmoothingFactor;
long long _lastTotalCount = 0;
boost::optional<double> _lastAvgCount;
};
/**
* Controls the per-second rate at which queries against a collection are sampled on this
* sampler. Uses token bucket.
*/
class SampleRateLimiter {
public:
static constexpr double kEpsilon = 0.001;
SampleRateLimiter(ServiceContext* serviceContext,
const NamespaceString& nss,
const UUID& collUuid,
double numTokensPerSecond)
: _serviceContext(serviceContext),
_nss(nss),
_collUuid(collUuid),
_numTokensPerSecond(numTokensPerSecond) {
invariant(_numTokensPerSecond > 0);
_lastRefillTime = _serviceContext->getFastClockSource()->now();
};
const NamespaceString& getNss() const {
return _nss;
}
const UUID& getCollectionUuid() const {
return _collUuid;
}
double getRate() const {
return _numTokensPerSecond;
}
double getBurstCapacity() const {
return _getBurstCapacity(_numTokensPerSecond);
}
/**
* Requests to consume one token from the bucket. Causes the bucket to be refilled with
* tokens created since last refill time. Does not block if the bucket is empty or there is
* fewer than one token in the bucket. Returns true if a token has been consumed
* successfully, and false otherwise.
*/
bool tryConsume();
/**
* Sets a new rate. Causes the bucket to be refilled with tokens created since last refill
* time according to the previous rate.
*/
void refreshRate(double numTokensPerSecond);
private:
/**
* Returns the maximum of number of tokens that a bucket with given rate can store at any
* given time.
*/
static double _getBurstCapacity(double numTokensPerSecond);
/**
* Fills the bucket with tokens created since last refill time according to the given rate
* and burst capacity.
*/
void _refill(double numTokensPerSecond, double burstCapacity);
const ServiceContext* _serviceContext;
const NamespaceString _nss;
const UUID _collUuid;
double _numTokensPerSecond;
// The bucket is only refilled when there is a consume request or a rate refresh.
Date_t _lastRefillTime;
double _lastNumTokens = 0;
};
QueryAnalysisSampler() = default;
~QueryAnalysisSampler() = default;
QueryAnalysisSampler(QueryAnalysisSampler&& source) = delete;
QueryAnalysisSampler& operator=(QueryAnalysisSampler&& other) = delete;
/**
* Obtains the service-wide QueryAnalysisSampler instance.
*/
static QueryAnalysisSampler& get(OperationContext* opCtx);
static QueryAnalysisSampler& get(ServiceContext* serviceContext);
void onStartup();
void onShutdown();
/**
* Returns true if a query should be sampled, and false otherwise. Can only be invoked once on
* for each query since it decrements the number remaining queries to sample if this query
* should be sampled.
*/
bool shouldSample(const NamespaceString& nss);
void refreshQueryStatsForTest() {
_refreshQueryStats();
}
QueryStats getQueryStatsForTest() const {
stdx::lock_guard<Latch> lk(_mutex);
return _queryStats;
}
void refreshConfigurationsForTest(OperationContext* opCtx) {
_refreshConfigurations(opCtx);
}
std::map<NamespaceString, SampleRateLimiter> getRateLimitersForTest() const {
stdx::lock_guard<Latch> lk(_mutex);
return _sampleRateLimiters;
}
private:
void _refreshQueryStats();
void _refreshConfigurations(OperationContext* opCtx);
mutable Mutex _mutex = MONGO_MAKE_LATCH("QueryAnalysisSampler::_mutex");
PeriodicJobAnchor _periodicQueryStatsRefresher;
QueryStats _queryStats;
PeriodicJobAnchor _periodicConfigurationsRefresher;
std::map<NamespaceString, SampleRateLimiter> _sampleRateLimiters;
};
} // namespace analyze_shard_key
} // namespace mongo
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