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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 <boost/intrusive_ptr.hpp>
#include "mongo/base/string_data.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/db/aggregated_index_usage_tracker.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/util/intrusive_counter.h"
#include "mongo/util/string_map.h"
#include "mongo/util/time_support.h"
namespace mongo {
class ClockSource;
class ServiceContext;
/**
* CollectionIndexUsageTracker tracks index usage statistics for a collection. An index is
* considered "used" when it appears as part of a winning plan for an operation that uses the
* query system.
*
* It also tracks non-usage of indexes. I.e. it collects information about collection scans that
* occur on a collection.
*
* Indexes must be registered and deregistered on creation/destruction.
*
* Internally concurrency safe for multiple callers concurrently but with only a SINGLE caller of
* either registerIndex() or unregisterIndex() at a time. Callers of registerIndex() and
* unregisterIndex() must hold an exclusive collection lock to ensure serialization.
*/
class CollectionIndexUsageTracker {
CollectionIndexUsageTracker(const CollectionIndexUsageTracker&) = delete;
CollectionIndexUsageTracker& operator=(const CollectionIndexUsageTracker&) = delete;
public:
struct CollectionScanStats {
unsigned long long collectionScans{0};
unsigned long long collectionScansNonTailable{0};
};
struct IndexUsageStats : public RefCountable {
IndexUsageStats() = default;
explicit IndexUsageStats(Date_t now, const BSONObj& key, const IndexFeatures& idxFeatures)
: trackerStartTime(now), indexKey(key.getOwned()), features(idxFeatures) {}
IndexUsageStats(const IndexUsageStats& other)
: accesses(other.accesses.load()),
trackerStartTime(other.trackerStartTime),
indexKey(other.indexKey),
features(other.features) {}
IndexUsageStats& operator=(const IndexUsageStats& other) {
accesses.store(other.accesses.load());
trackerStartTime = other.trackerStartTime;
indexKey = other.indexKey;
features = other.features;
return *this;
}
// Number of operations that have used this index.
AtomicWord<long long> accesses;
// Date/Time that we started tracking index usage.
Date_t trackerStartTime;
// An owned copy of the associated IndexDescriptor's index key.
BSONObj indexKey;
// Features in use by this index for global feature usage tracking.
IndexFeatures features;
};
/**
* The IndexUsageStats entries are stored in the map as pointers so that concurrent updates to
* an entry's internal values are retained across map copies rather than lost. intrusive_ptrs
* are used rather than shared_ptrs because: intrusive_ptrs are more performant when copies are
* made; and the usage is encapsulated by this class and not externally exposed.
*/
using CollectionIndexUsageMap = StringMap<boost::intrusive_ptr<IndexUsageStats>>;
/**
* Constructs a CollectionIndexUsageTracker.
*
* Does not take ownership of 'clockSource'. 'clockSource' must refer to a non-null clock
* source that is valid for the lifetime of the constructed CollectionIndexUsageTracker.
*/
explicit CollectionIndexUsageTracker(AggregatedIndexUsageTracker* aggregatedIndexUsageTracker,
ClockSource* clockSource);
/**
* Record that an operation used index 'indexName'. Safe to be called by multiple threads
* concurrently.
*/
void recordIndexAccess(StringData indexName);
/**
* Add map entry for 'indexName' stats collection.
*
* Must be called under an exclusive collection lock in order to serialize calls to
* registerIndex() and unregisterIndex().
*/
void registerIndex(StringData indexName,
const BSONObj& indexKey,
const IndexFeatures& features);
/**
* Erase statistics for index 'indexName'. Can be safely called even if indexName is not
* registered, which is possible under certain failure scenarios.
*
* Must be called under an exclusive collection lock in order to serialize calls to
* registerIndex() and unregisterIndex().
*/
void unregisterIndex(StringData indexName);
/**
* Get the current state of the usage statistics map. This map will only include indexes that
* exist at the time of calling.
*/
std::shared_ptr<CollectionIndexUsageMap> getUsageStats() const;
/**
* Get the current state of the usage of collection scans. This struct will only include
* information about the collection scans that have occured at the time of calling.
*
* Can be safely called by multiple threads concurrently.
*/
CollectionScanStats getCollectionScanStats() const;
/**
* Records that an operation did a collection scan.
*
* Can be safely called by multiple threads concurrently.
*/
void recordCollectionScans(unsigned long long collectionScans);
void recordCollectionScansNonTailable(unsigned long long collectionScansNonTailable);
private:
// Maps index name to index usage statistics.
//
// NOTE: This map must only be accessed via atomic_load and atomic_store!
//
// Internal concurrency control is ensured by always using atomic_load/store on this shared_ptr.
// The map should never be modified outside the protection of atomic_load/atomic_store.
std::shared_ptr<CollectionIndexUsageMap> _indexUsageStatsMap;
// Clock source. Used when the 'trackerStartTime' time for an IndexUsageStats object needs to
// be set.
ClockSource* _clockSource;
// All CollectionIndexUsageTrackers also update the AggregatedIndexUsageTracker to report
// globally aggregated index statistics for the server.
AggregatedIndexUsageTracker* _aggregatedIndexUsageTracker;
AtomicWord<unsigned long long> _collectionScans{0};
AtomicWord<unsigned long long> _collectionScansNonTailable{0};
};
} // namespace mongo
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