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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 <functional>
#include <vector>
#include "mongo/util/string_map.h"
namespace mongo {
class BSONObj;
class CollatorInterface;
class CompositeIndexabilityDiscriminator;
class MatchExpression;
struct CoreIndexInfo;
namespace projection_executor {
class ProjectionExecutor;
}
using IndexabilityDiscriminator = std::function<bool(const MatchExpression* me)>;
using IndexabilityDiscriminators = std::vector<IndexabilityDiscriminator>;
using IndexToDiscriminatorMap = StringMap<CompositeIndexabilityDiscriminator>;
using PathDiscriminatorsMap = StringMap<IndexToDiscriminatorMap>;
/**
* CompositeIndexabilityDiscriminator holds all indexability discriminators for a particular path,
* for a particular index. For example, a path may have both a collation discriminator and a sparse
* index discriminator for a particular index.
*/
class CompositeIndexabilityDiscriminator {
public:
/**
* Considers all discriminators for the path-index pair, and returns a single bit indicating
* whether the index can be used for that path.
*/
bool isMatchCompatibleWithIndex(const MatchExpression* me) const {
for (auto&& discriminator : _discriminators) {
if (!discriminator(me)) {
return false;
}
}
return true;
}
void addDiscriminator(IndexabilityDiscriminator discriminator) {
_discriminators.push_back(std::move(discriminator));
}
private:
IndexabilityDiscriminators _discriminators;
};
/**
* PlanCacheIndexabilityState holds a set of "indexability discriminators. An indexability
* discriminator is a binary predicate function, used to classify match expressions based on the
* data values in the expression.
*
* These discriminators are used to distinguish between queries of a similar shape but not the same
* candidate indexes. So each discriminator typically represents a decision like "is this index
* valid?" or "does this piece of the query disqualify it from using this index?". The output of
* these decisions is included in the plan cache key.
*/
class PlanCacheIndexabilityState {
PlanCacheIndexabilityState(const PlanCacheIndexabilityState&) = delete;
PlanCacheIndexabilityState& operator=(const PlanCacheIndexabilityState&) = delete;
public:
PlanCacheIndexabilityState() = default;
/**
* Returns a map from index name to discriminator for each index associated with 'path'.
* Returns an empty set if no discriminators are registered for 'path'.
*
* The object returned by reference is valid until the next call to updateDiscriminators() or
* until destruction of 'this', whichever is first.
*/
const IndexToDiscriminatorMap& getPathDiscriminators(StringData path) const;
/**
* Returns a map of index name to discriminator set. These discriminators are not
* associated with a particular path of a query and apply to the entire MatchExpression.
*/
const IndexToDiscriminatorMap& getGlobalDiscriminators() const {
return _globalDiscriminatorMap;
}
/**
* Construct an IndexToDiscriminator map for the given path, only for the wildcard indexes
* which have been included in the indexability state.
*/
IndexToDiscriminatorMap buildWildcardDiscriminators(StringData path) const;
/**
* Clears discriminators for all paths, and regenerates them from 'indexCores'.
*/
void updateDiscriminators(const std::vector<CoreIndexInfo>& indexCores);
private:
/**
* A $** index may index an infinite number of fields. We cannot just store a discriminator for
* every possible field that it indexes, so we have to maintain some special context about the
* index.
*/
struct WildcardIndexDiscriminatorContext {
WildcardIndexDiscriminatorContext(projection_executor::ProjectionExecutor* proj,
std::string name,
const CollatorInterface* coll)
: projectionExec(proj), collator(coll), catalogName(std::move(name)) {}
// These are owned by the catalog.
projection_executor::ProjectionExecutor* projectionExec;
const CollatorInterface* collator;
std::string catalogName;
};
/**
* Adds sparse index discriminators for the sparse index with the given key pattern to
* '_pathDiscriminatorsMap'.
*
* A sparse index discriminator distinguishes equality matches to null from other expression
* types. For example, this allows the predicate {a: 1} to be considered of a different
* shape from the predicate {a: null}, if there is a sparse index defined with "a" as an
* element of the key pattern. The former predicate is compatibile with this index, but the
* latter is not compatible.
*/
void processSparseIndex(const std::string& indexName, const BSONObj& keyPattern);
/**
* Adds a global discriminator for the partial index with the given filter expression
* to the discriminators for that index in '_globalDiscriminatorMap'.
*
* A partial index discriminator distinguishes expressions that match a given partial index
* predicate from expressions that don't match the partial index predicate. For example,
* this allows the predicate {a: {$gt: 5}} to be considered a different shape than the
* predicate {a: {$gt: -5}}, if there is a partial index defined with document filter {a:
* {$gt: 0}}. The former is compatible with this index, but the latter is not compatible.
*/
void processPartialIndex(const std::string& indexName, const MatchExpression* filterExpr);
/**
* Adds collation discriminators for the index with the given key pattern and collator to
* '_pathDiscriminatorsMap'.
*
* The discriminator for a given path returns true if the index collator matches the query
* collator, or if the query does not contain string comparison at that path.
*/
void processIndexCollation(const std::string& indexName,
const BSONObj& keyPattern,
const CollatorInterface* collator);
/**
* Adds special state for a $** index. When the discriminators are retrieved for a certain
* path, appropriate discriminators for the wildcard index will be included if it includes the
* given path.
*/
void processWildcardIndex(const CoreIndexInfo& cii);
// PathDiscriminatorsMap is a map from field path to index name to IndexabilityDiscriminator.
PathDiscriminatorsMap _pathDiscriminatorsMap;
// Map from index name to global discriminators. These are discriminators which do not apply to
// a single path but the entire MatchExpression.
IndexToDiscriminatorMap _globalDiscriminatorMap;
std::vector<WildcardIndexDiscriminatorContext> _wildcardIndexDiscriminators;
};
} // namespace mongo
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