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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/query/canonical_query.h"
#include "mongo/db/query/index_entry.h"
#include "mongo/db/query/query_solution.h"
namespace mongo {
/**
* QueryPlanner's job is to provide an entry point to the query planning and optimization
* process.
*/
class QueryPlanner {
public:
enum Options {
// You probably want to set this.
DEFAULT = 0,
// Set this if you don't want a table scan.
// See http://docs.mongodb.org/manual/reference/parameters/
NO_TABLE_SCAN = 1,
// Set this if you want a collscan outputted even if there's an ixscan.
INCLUDE_COLLSCAN = 2,
};
/**
* Outputs a series of possible solutions for the provided 'query' into 'out'. Uses the
* provided indices to generate a solution.
*
* Caller owns pointers in *out.
*/
static void plan(const CanonicalQuery& query,
const vector<IndexEntry>& indices,
size_t options,
vector<QuerySolution*>* out);
private:
//
// Index Selection methods.
//
/**
* Return all the fields in the tree rooted at 'node' that we can use an index on
* in order to answer the query.
*
* The 'prefix' argument is a path prefix to be prepended to any fields mentioned in
* predicates encountered. Some array operators specify a path prefix.
*/
static void getFields(MatchExpression* node, string prefix, unordered_set<string>* out);
/**
* Find all indices prefixed by fields we have predicates over. Only these indices are
* useful in answering the query.
*/
static void findRelevantIndices(const unordered_set<string>& fields,
const vector<IndexEntry>& indices,
vector<IndexEntry>* out);
/**
* Return true if the index key pattern field 'elt' (which belongs to 'index') can be used
* to answer the predicate 'node'.
*
* For example, {field: "hashed"} can only be used with sets of equalities.
* {field: "2d"} can only be used with some geo predicates.
* {field: "2dsphere"} can only be used with some other geo predicates.
*/
static bool compatible(const BSONElement& elt, const IndexEntry& index, MatchExpression* node);
/**
* Determine how useful all of our relevant 'indices' are to all predicates in the subtree
* rooted at 'node'. Affixes a RelevantTag to all predicate nodes which can use an index.
*
* 'prefix' is a path prefix that should be prepended to any path (certain array operators
* imply a path prefix).
*
* For an index to be useful to a predicate, the index must be compatible (see above).
*
* If an index is prefixed by the predicate's path, it's always useful.
*
* If an index is compound but not prefixed by a predicate's path, it's only useful if
* there exists another predicate that 1. will use that index and 2. is related to the
* original predicate by having an AND as a parent.
*/
static void rateIndices(MatchExpression* node, string prefix,
const vector<IndexEntry>& indices);
//
// Collection Scan Data Access method.
//
/**
* Return a CollectionScanNode that scans as requested in 'query'.
*/
static QuerySolution* makeCollectionScan(const CanonicalQuery& query, bool tailable);
//
// Indexed Data Access methods.
//
// The inArrayOperator flag deserves some attention. It is set when we're processing a child of
// a MatchExpression::ALL or MatchExpression::ELEM_MATCH_OBJECT.
//
// When true, the following behavior changes for all methods below that take it as an argument:
// 0. No deletion of MatchExpression(s). In fact,
// 1. No mutation of the MatchExpression at all. We need the tree as-is in order to perform
// a filter on the entire tree.
// 2. No fetches performed. There will be a final fetch by the caller of buildIndexedDataAccess
// who set the value of inArrayOperator to true.
// 3. No compound indices are used and no bounds are combined. These are incorrect in the context
// of these operators.
//
/**
* If 'inArrayOperator' is false, takes ownership of 'root'.
*/
static QuerySolutionNode* buildIndexedDataAccess(MatchExpression* root,
bool inArrayOperator,
const vector<IndexEntry>& indices);
/**
* Takes ownership of 'root'.
*/
static QuerySolutionNode* buildIndexedAnd(MatchExpression* root,
bool inArrayOperator,
const vector<IndexEntry>& indices);
/**
* Takes ownership of 'root'.
*/
static QuerySolutionNode* buildIndexedOr(MatchExpression* root,
bool inArrayOperator,
const vector<IndexEntry>& indices);
/**
* Helper used by buildIndexedAnd and buildIndexedOr.
*
* The children of AND and OR nodes are sorted by the index that the subtree rooted at
* that node uses. Child nodes that use the same index are adjacent to one another to
* facilitate grouping of index scans. As such, the processing for AND and OR is
* almost identical.
*
* See tagForSort and sortUsingTags in index_tag.h for details on ordering the children
* of OR and AND.
*
* Does not take ownership of 'root' but may remove children from it.
*/
static bool processIndexScans(MatchExpression* root,
bool inArrayOperator,
const vector<IndexEntry>& indices,
vector<QuerySolutionNode*>* out);
//
// Helpers for creating an index scan.
//
/**
* Create a new data access node.
*
* If the node is an index scan, the bounds for 'expr' are computed and placed into the
* first field's OIL position. The rest of the OILs are allocated but uninitialized.
*
* If the node is a geo node, XXX.
*/
static QuerySolutionNode* makeLeafNode(const BSONObj& indexKeyPattern,
MatchExpression* expr,
bool* exact);
/**
* Merge the predicate 'expr' with the leaf node 'node'.
*/
static void mergeWithLeafNode(MatchExpression* expr, const BSONObj& keyPattern,
size_t pos, bool* exactOut, QuerySolutionNode* node);
/**
* If index scan, fill in any bounds that are missing in 'node' with the "all values for
* this field" interval.
*
* If geo, XXX.
*/
static void finishLeafNode(QuerySolutionNode* node, const BSONObj& indexKeyPattern);
//
// Analysis of Data Access
//
/**
* In brief: performs sort and covering analysis.
*
* The solution rooted at 'solnRoot' provides data for the query, whether through some
* configuration of indices or through a collection scan. Additional stages may be required
* to perform sorting, projection, or other operations that are independent of the source
* of the data. These stages are added atop 'solnRoot'.
*
* 'taggedRoot' is a copy of the parse tree. Nodes in 'solnRoot' may point into it.
*
* Takes ownership of 'solnRoot' and 'taggedRoot'.
*
* Caller owns the returned QuerySolution.
*/
static QuerySolution* analyzeDataAccess(const CanonicalQuery& query,
QuerySolutionNode* solnRoot);
};
} // namespace mongo
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