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/**
* Copyright (C) 2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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/optional/optional.hpp>
#include <set>
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/index_tag.h"
#include "mongo/db/query/lru_key_value.h"
#include "mongo/db/query/plan_cache_indexability.h"
#include "mongo/db/query/query_planner_params.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/stdx/mutex.h"
namespace mongo {
// A PlanCacheKey is a string-ified version of a query's predicate/projection/sort.
typedef std::string PlanCacheKey;
struct PlanRankingDecision;
struct QuerySolution;
struct QuerySolutionNode;
/**
* When the CachedPlanStage runs a cached query, it can provide feedback to the cache. This
* feedback is available to anyone who retrieves that query in the future.
*/
struct PlanCacheEntryFeedback {
// How well did the cached plan perform?
std::unique_ptr<PlanStageStats> stats;
// The "goodness" score produced by the plan ranker
// corresponding to 'stats'.
double score;
};
// TODO: Replace with opaque type.
typedef std::string PlanID;
/**
* A PlanCacheIndexTree is the meaty component of the data
* stored in SolutionCacheData. It is a tree structure with
* index tags that indicates to the access planner which indices
* it should try to use.
*
* How a PlanCacheIndexTree is created:
* The query planner tags a match expression with indices. It
* then uses the tagged tree to create a PlanCacheIndexTree,
* using QueryPlanner::cacheDataFromTaggedTree. The PlanCacheIndexTree
* is isomorphic to the tagged match expression, and has matching
* index tags.
*
* How a PlanCacheIndexTree is used:
* When the query planner is planning from the cache, it uses
* the PlanCacheIndexTree retrieved from the cache in order to
* recreate index assignments. Specifically, a raw MatchExpression
* is tagged according to the index tags in the PlanCacheIndexTree.
* This is done by QueryPlanner::tagAccordingToCache.
*/
struct PlanCacheIndexTree {
PlanCacheIndexTree() : entry(nullptr), index_pos(0), canCombineBounds(true) {}
~PlanCacheIndexTree() {
for (std::vector<PlanCacheIndexTree*>::const_iterator it = children.begin();
it != children.end();
++it) {
delete *it;
}
}
/**
* Clone 'ie' and set 'this->entry' to be the clone.
*/
void setIndexEntry(const IndexEntry& ie);
/**
* Make a deep copy.
*/
PlanCacheIndexTree* clone() const;
/**
* For debugging.
*/
std::string toString(int indents = 0) const;
// Children owned here.
std::vector<PlanCacheIndexTree*> children;
// Owned here.
std::unique_ptr<IndexEntry> entry;
size_t index_pos;
// The value for this member is taken from the IndexTag of the corresponding match expression
// and is used to ensure that bounds are correctly intersected and/or compounded when a query is
// planned from the plan cache.
bool canCombineBounds;
};
/**
* Data stored inside a QuerySolution which can subsequently be
* used to create a cache entry. When this data is retrieved
* from the cache, it is sufficient to reconstruct the original
* QuerySolution.
*/
struct SolutionCacheData {
SolutionCacheData()
: tree(nullptr),
solnType(USE_INDEX_TAGS_SOLN),
wholeIXSolnDir(1),
indexFilterApplied(false) {}
// Make a deep copy.
SolutionCacheData* clone() const;
// For debugging.
std::string toString() const;
// Owned here. If 'wholeIXSoln' is false, then 'tree'
// can be used to tag an isomorphic match expression. If 'wholeIXSoln'
// is true, then 'tree' is used to store the relevant IndexEntry.
// If 'collscanSoln' is true, then 'tree' should be NULL.
std::unique_ptr<PlanCacheIndexTree> tree;
enum SolutionType {
// Indicates that the plan should use
// the index as a proxy for a collection
// scan (e.g. using index to provide sort).
WHOLE_IXSCAN_SOLN,
// The cached plan is a collection scan.
COLLSCAN_SOLN,
// Build the solution by using 'tree'
// to tag the match expression.
USE_INDEX_TAGS_SOLN
} solnType;
// The direction of the index scan used as
// a proxy for a collection scan. Used only
// for WHOLE_IXSCAN_SOLN.
int wholeIXSolnDir;
// True if index filter was applied.
bool indexFilterApplied;
};
class PlanCacheEntry;
/**
* Information returned from a get(...) query.
*/
class CachedSolution {
private:
MONGO_DISALLOW_COPYING(CachedSolution);
public:
CachedSolution(const PlanCacheKey& key, const PlanCacheEntry& entry);
~CachedSolution();
// Owned here.
std::vector<SolutionCacheData*> plannerData;
// Key used to provide feedback on the entry.
PlanCacheKey key;
// For debugging.
std::string toString() const;
// We are extracting just enough information from the canonical
// query. We could clone the canonical query but the following
// items are all that is displayed to the user.
BSONObj query;
BSONObj sort;
BSONObj projection;
BSONObj collation;
// The number of work cycles taken to decide on a winning plan when the plan was first
// cached.
size_t decisionWorks;
};
/**
* Used by the cache to track entries and their performance over time.
* Also used by the plan cache commands to display plan cache state.
*/
class PlanCacheEntry {
private:
MONGO_DISALLOW_COPYING(PlanCacheEntry);
public:
/**
* Create a new PlanCacheEntry.
* Grabs any planner-specific data required from the solutions.
* Takes ownership of the PlanRankingDecision that placed the plan in the cache.
*/
PlanCacheEntry(const std::vector<QuerySolution*>& solutions, PlanRankingDecision* why);
~PlanCacheEntry();
/**
* Make a deep copy.
*/
PlanCacheEntry* clone() const;
// For debugging.
std::string toString() const;
//
// Planner data
//
// Data provided to the planner to allow it to recreate the solutions this entry
// represents. Each SolutionCacheData is fully owned here, so in order to return
// it from the cache a deep copy is made and returned inside CachedSolution.
std::vector<SolutionCacheData*> plannerData;
// TODO: Do we really want to just hold a copy of the CanonicalQuery? For now we just
// extract the data we need.
//
// Used by the plan cache commands to display an example query
// of the appropriate shape.
BSONObj query;
BSONObj sort;
BSONObj projection;
BSONObj collation;
//
// Performance stats
//
// Information that went into picking the winning plan and also why
// the other plans lost.
std::unique_ptr<PlanRankingDecision> decision;
// Annotations from cached runs. The CachedPlanStage provides these stats about its
// runs when they complete.
std::vector<PlanCacheEntryFeedback*> feedback;
};
/**
* Caches the best solution to a query. Aside from the (CanonicalQuery -> QuerySolution)
* mapping, the cache contains information on why that mapping was made and statistics on the
* cache entry's actual performance on subsequent runs.
*
*/
class PlanCache {
private:
MONGO_DISALLOW_COPYING(PlanCache);
public:
/**
* We don't want to cache every possible query. This function
* encapsulates the criteria for what makes a canonical query
* suitable for lookup/inclusion in the cache.
*/
static bool shouldCacheQuery(const CanonicalQuery& query);
/**
* If omitted, namespace set to empty string.
*/
PlanCache();
PlanCache(const std::string& ns);
~PlanCache();
/**
* Record solutions for query. Best plan is first element in list.
* Each query in the cache will have more than 1 plan because we only
* add queries which are considered by the multi plan runner (which happens
* only when the query planner generates multiple candidate plans).
*
* Takes ownership of 'why'.
*
* If the mapping was added successfully, returns Status::OK().
* If the mapping already existed or some other error occurred, returns another Status.
*/
Status add(const CanonicalQuery& query,
const std::vector<QuerySolution*>& solns,
PlanRankingDecision* why);
/**
* Look up the cached data access for the provided 'query'. Used by the query planner
* to shortcut planning.
*
* If there is no entry in the cache for the 'query', returns an error Status.
*
* If there is an entry in the cache, populates 'crOut' and returns Status::OK(). Caller
* owns '*crOut'.
*/
Status get(const CanonicalQuery& query, CachedSolution** crOut) const;
/**
* When the CachedPlanStage runs a plan out of the cache, we want to record data about the
* plan's performance. The CachedPlanStage calls feedback(...) after executing the cached
* plan for a trial period in order to do this.
*
* Cache takes ownership of 'feedback'.
*
* If the entry corresponding to 'cq' isn't in the cache anymore, the feedback is ignored
* and an error Status is returned.
*
* If the entry corresponding to 'cq' still exists, 'feedback' is added to the run
* statistics about the plan. Status::OK() is returned.
*/
Status feedback(const CanonicalQuery& cq, PlanCacheEntryFeedback* feedback);
/**
* Remove the entry corresponding to 'ck' from the cache. Returns Status::OK() if the plan
* was present and removed and an error status otherwise.
*/
Status remove(const CanonicalQuery& canonicalQuery);
/**
* Remove *all* cached plans. Does not clear index information.
*/
void clear();
/**
* Get the cache key corresponding to the given canonical query. The query need not already
* be cached.
*
* This is provided in the public API simply as a convenience for consumers who need some
* description of query shape (e.g. index filters).
*
* Callers must hold the collection lock when calling this method.
*/
PlanCacheKey computeKey(const CanonicalQuery&) const;
/**
* Returns a copy of a cache entry.
* Used by planCacheListPlans to display plan details.
*
* If there is no entry in the cache for the 'query', returns an error Status.
*
* If there is an entry in the cache, populates 'entryOut' and returns Status::OK(). Caller
* owns '*entryOut'.
*/
Status getEntry(const CanonicalQuery& cq, PlanCacheEntry** entryOut) const;
/**
* Returns a vector of all cache entries.
* Caller owns the result vector and is responsible for cleaning up
* the cache entry copies.
* Used by planCacheListQueryShapes and index_filter_commands_test.cpp.
*/
std::vector<PlanCacheEntry*> getAllEntries() const;
/**
* Returns true if there is an entry in the cache for the 'query'.
* Internally calls hasKey() on the LRU cache.
*/
bool contains(const CanonicalQuery& cq) const;
/**
* Returns number of entries in cache.
* Used for testing.
*/
size_t size() const;
/**
* Updates internal state kept about the collection's indexes. Must be called when the set
* of indexes on the associated collection have changed.
*
* Callers must hold the collection lock in exclusive mode when calling this method.
*/
void notifyOfIndexEntries(const std::vector<IndexEntry>& indexEntries);
private:
void encodeKeyForMatch(const MatchExpression* tree, StringBuilder* keyBuilder) const;
void encodeKeyForSort(const BSONObj& sortObj, StringBuilder* keyBuilder) const;
void encodeKeyForProj(const BSONObj& projObj, StringBuilder* keyBuilder) const;
LRUKeyValue<PlanCacheKey, PlanCacheEntry> _cache;
// Protects _cache.
mutable stdx::mutex _cacheMutex;
// Counter for write notifications since initialization or last clear() invocation. Starts
// at 0.
AtomicInt32 _writeOperations;
// Full namespace of collection.
std::string _ns;
// Holds computed information about the collection's indexes. Used for generating plan
// cache keys.
//
// Concurrent access is synchronized by the collection lock. Multiple concurrent readers
// are allowed.
PlanCacheIndexabilityState _indexabilityState;
};
} // namespace mongo
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