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/**
* Copyright (C) 2013 10gen 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 "mongo/db/exec/plan_stats.h"
#include "mongo/db/query/plan_ranker.h"
#include "mongo/db/query/query_solution.h"
namespace mongo {
/**
* TODO: Debug commands:
* 1. show canonical form of query
* 2. show plans generated for query without (and with) cache
* 3. print out cache.
* 4. clear all elements from cache / otherwise manipulate cache.
*/
/**
* When the CachedPlanRunner 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 CachedSolutionFeedback {
PlanStageStats* stats;
};
/**
* A cached solution to a query.
*/
struct CachedSolution {
~CachedSolution() {
for (size_t i = 0; i < feedback.size(); ++i) {
delete feedback[i];
}
}
// The best solution for the CanonicalQuery.
scoped_ptr<QuerySolution> solution;
// Why the best solution was picked.
scoped_ptr<PlanRankingDecision> decision;
// Annotations from cached runs.
// TODO: How many of these do we really want to keep?
vector<CachedSolutionFeedback*> feedback;
private:
MONGO_DISALLOW_COPYING(CachedSolution);
};
/**
* 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 {
public:
/**
* Get the (global) cache for the provided namespace. Must not be held across yields.
* As such, there is no locking required.
*/
static PlanCache* get(const string& ns) { return NULL; }
/**
* Record 'solution' as the best plan for 'query' which was picked for reasons detailed in
* 'why'.
*
* Takes ownership of all arguments.
*
* If the mapping was added successfully, returns true.
* If the mapping already existed or some other error occurred, returns false;
*/
bool add(CanonicalQuery* query, QuerySolution* solution, PlanRankingDecision* why) {
return false;
}
/**
* Look up the cached solution for the provided query. If a cached solution exists, return
* a copy of it which the caller then owns. If no cached solution exists, returns NULL.
*
* TODO: Allow querying for exact query and querying for the shape of the query.
*/
CachedSolution* get(const CanonicalQuery& query) {
return NULL;
}
/**
* When the CachedPlanRunner runs a plan out of the cache, we want to record data about the
* plan's performance. Cache takes ownership of 'feedback'.
*
* If the (query, solution) pair isn't in the cache, the cache deletes feedback and returns
* false. Otherwise, returns true.
*/
bool feedback(const CanonicalQuery& query, const QuerySolution& solution,
const CachedSolutionFeedback* feedback) {
return false;
}
/**
* Remove the (query, solution) pair from our cache. Returns true if the plan was removed,
* false if it wasn't found.
*/
bool remove(const CanonicalQuery& query, const QuerySolution& solution) {
return false;
}
};
} // namespace mongo
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