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/**
* Copyright (C) 2021-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/functional/hash.hpp>
#include "mongo/db/exec/sbe/stages/stages.h"
#include "mongo/db/hasher.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/query/plan_cache.h"
#include "mongo/db/query/plan_cache_key_info.h"
#include "mongo/db/query/sbe_stage_builder.h"
#include "mongo/db/service_context.h"
namespace mongo {
namespace sbe {
/**
* Represents the sharding epoch of the collection which entry will be stored in the plan cache. The
* sharding epoch is not updated on operations like chunk splits and moves but rather on sharding
* and refine shard key operations.
*/
struct PlanCacheKeyShardingEpoch {
bool operator==(const PlanCacheKeyShardingEpoch& other) const {
return epoch == other.epoch && ts == other.ts;
}
OID epoch;
Timestamp ts;
};
/**
* Represents the "key" used in the PlanCache mapping from query shape -> query plan.
*/
class PlanCacheKey {
public:
PlanCacheKey(PlanCacheKeyInfo&& info,
UUID collectionUuid,
size_t collectionVersion,
boost::optional<Timestamp> newestVisibleIndexTimestamp,
boost::optional<PlanCacheKeyShardingEpoch> shardVersion)
: _info{std::move(info)},
_collectionUuid{collectionUuid},
_collectionVersion{collectionVersion},
_newestVisibleIndexTimestamp{newestVisibleIndexTimestamp},
_shardVersion{shardVersion} {}
const UUID& getCollectionUuid() const {
return _collectionUuid;
}
size_t getCollectionVersion() const {
return _collectionVersion;
}
bool operator==(const PlanCacheKey& other) const {
return other._collectionVersion == _collectionVersion &&
other._collectionUuid == _collectionUuid &&
other._newestVisibleIndexTimestamp == _newestVisibleIndexTimestamp &&
other._info == _info && other._shardVersion == _shardVersion;
}
bool operator!=(const PlanCacheKey& other) const {
return !(*this == other);
}
uint32_t queryHash() const {
return _info.queryHash();
}
uint32_t planCacheKeyHash() const {
size_t hash = _info.planCacheKeyHash();
boost::hash_combine(hash, UUID::Hash{}(_collectionUuid));
boost::hash_combine(hash, _collectionVersion);
if (_newestVisibleIndexTimestamp) {
boost::hash_combine(hash, _newestVisibleIndexTimestamp->asULL());
}
if (_shardVersion) {
_shardVersion->epoch.hash_combine(hash);
boost::hash_combine(hash, _shardVersion->ts.asULL());
}
return hash;
}
const std::string& toString() const {
return _info.toString();
}
private:
// Contains the actual encoding of the query shape as well as the index discriminators.
const PlanCacheKeyInfo _info;
const UUID _collectionUuid;
// There is a special collection versioning scheme associated with the SBE plan cache. Whenever
// an action against a collection is made which should invalidate the plan cache entries for the
// collection -- in particular index builds and drops -- the version number is incremented.
// Readers specify the version number that they are reading at so that they only pick up cache
// entries with the right set of indexes.
//
// We also clean up all cache entries for a particular (collectionUuid, versionNumber) pair when
// all readers seeing this version of the collection have drained.
const size_t _collectionVersion;
// The '_collectionVersion' is not currently sufficient in order to ensure that the indexes
// visible to the reader are consistent with the indexes present in the cache entry. The reason
// is that all readers see the latest copy-on-write version of the 'Collection' object, even
// though they are allowed to read at an older timestamp, potentially at a time before an index
// build completed.
//
// To solve this problem, we incorporate the timestamp of the newest index visible to the reader
// into the plan cache key. This ensures that the set of indexes visible to the reader match
// those present in the plan cache entry, preventing a situation where the plan cache entry
// reflects a newer version of the index catalog than the one visible to the reader.
//
// In the future, this could instead be solved with point-in-time catalog lookups.
const boost::optional<Timestamp> _newestVisibleIndexTimestamp;
// Ensures that a cached SBE plan cannot be reused if the collection has since become sharded or
// changed its shard key. The cached plan may no longer be valid after sharding or shard key
// refining since the structure of the plan depends on whether the collection is sharded, and if
// sharded depends on the shard key.
const boost::optional<PlanCacheKeyShardingEpoch> _shardVersion;
};
class PlanCacheKeyHasher {
public:
std::size_t operator()(const PlanCacheKey& k) const {
return k.planCacheKeyHash();
}
};
struct PlanCachePartitioner {
// Determines the partitioning function for use with the 'Partitioned' utility.
std::size_t operator()(const PlanCacheKey& k, const std::size_t nPartitions) const {
return PlanCacheKeyHasher{}(k) % nPartitions;
}
};
/**
* Represents the data cached in the SBE plan cache. This data holds an execution plan and necessary
* auxiliary data for preparing and executing the PlanStage tree.
*/
struct CachedSbePlan {
CachedSbePlan(std::unique_ptr<sbe::PlanStage> root, stage_builder::PlanStageData data)
: root(std::move(root)), planStageData(std::move(data)) {
tassert(5968206, "The RuntimeEnvironment should not be null", planStageData.env);
}
std::unique_ptr<CachedSbePlan> clone() const {
return std::make_unique<CachedSbePlan>(root->clone(), planStageData);
}
uint64_t estimateObjectSizeInBytes() const {
return root->estimateCompileTimeSize();
}
std::unique_ptr<sbe::PlanStage> root;
stage_builder::PlanStageData planStageData;
bool indexFilterApplied = false;
};
using PlanCacheEntry = PlanCacheEntryBase<CachedSbePlan, plan_cache_debug_info::DebugInfoSBE>;
struct BudgetEstimator {
size_t operator()(const std::shared_ptr<const PlanCacheEntry>& entry) {
return entry->estimatedEntrySizeBytes;
}
};
using PlanCache = PlanCacheBase<PlanCacheKey,
CachedSbePlan,
BudgetEstimator,
plan_cache_debug_info::DebugInfoSBE,
PlanCachePartitioner,
PlanCacheKeyHasher>;
/**
* A helper method to get the global SBE plan cache decorated in 'serviceCtx'.
*/
PlanCache& getPlanCache(ServiceContext* serviceCtx);
/**
* A wrapper for the helper above. 'opCtx' cannot be null.
*/
PlanCache& getPlanCache(OperationContext* opCtx);
/**
* Removes cached plan entries with the given collection UUID and collection version number.
*/
void clearPlanCacheEntriesWith(ServiceContext* serviceCtx,
UUID collectionUuid,
size_t collectionVersion);
} // namespace sbe
} // namespace mongo
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