mongodb/db/queryoptimizer.h

/* queryoptimizer.h */

/**
*    Copyright (C) 2008 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/>.
*/

#pragma once

#include "cursor.h"
#include "jsobj.h"
#include "queryutil.h"

namespace mongo {
    
    class IndexDetails;
    class QueryPlan {
    public:
        QueryPlan( const FieldBoundSet &fbs, const BSONObj &order, const IndexDetails *index = 0 );
        QueryPlan( const QueryPlan &other );
        /* If true, no other index can do better. */
        bool optimal() const { return optimal_; }
        /* ScanAndOrder processing will be required if true */
        bool scanAndOrderRequired() const { return scanAndOrderRequired_; }
        /* When true, the index we are using has keys such that it can completely resolve the
         query expression to match by itself without ever checking the main object.
         */
        bool keyMatch() const { return keyMatch_; }
        /* True if keyMatch() is true, and all matches will be equal according to woEqual() */
        bool exactKeyMatch() const { return exactKeyMatch_; }
        /* If true, the startKey and endKey are unhelpful, the index order doesn't match the 
           requested sort order, and keyMatch is false */
        bool unhelpful() const { return unhelpful_; }
        int direction() const { return direction_; }
        BSONObj startKey() const { return startKey_; }
        BSONObj endKey() const { return endKey_; }
        auto_ptr< Cursor > newCursor() const;
        BSONObj indexKey() const;
        const char *ns() const { return fbs_.ns(); }
        BSONObj query() const { return fbs_.query(); }
    private:
        const FieldBoundSet &fbs_;
        const BSONObj &order_;
        const IndexDetails *index_;
        bool optimal_;
        bool scanAndOrderRequired_;
        bool keyMatch_;
        bool exactKeyMatch_;
        int direction_;
        BSONObj startKey_;
        BSONObj endKey_;
        bool unhelpful_;
    };

    class QueryAborter {
    public:
        QueryAborter( const bool &firstDone ) :
        firstDone_( firstDone ){}
        class AbortException : public std::exception {
        };
        void mayAbort() const {
            if ( firstDone_ )
                throw AbortException();
        }
    private:
        const bool &firstDone_;
    };
    
    // Inherit from this interface to implement a new query operation.
    class QueryOp {
    public:
        QueryOp() : complete_() {}
        virtual ~QueryOp() {}
        // Called by the runner, to execute this query operation using the
        // given query plan.  The implementation should call qa.mayAbort()
        // periodically in order to abort if the operation on another query
        // plan is complete.
        virtual void run( const QueryPlan &qp, const QueryAborter &qa ) = 0;
        // Return a copy of the inheriting class, which will be run with its own
        // query plan.
        virtual QueryOp *clone() const = 0;
        bool complete() const { return complete_; }
        string exceptionMessage() const { return exceptionMessage_; }
        // To be called by the runner only.
        void setComplete() { complete_ = true; }
        // To be called by the runner only.
        void setExceptionMessage( const string &exceptionMessage ) { exceptionMessage_ = exceptionMessage; }
    private:
        bool complete_;
        string exceptionMessage_;
    };
    
    class QueryPlanSet {
    public:
        QueryPlanSet( const char *ns, const BSONObj &query, const BSONObj &order, const BSONElement *hint = 0 );
        int nPlans() const { return plans_.size(); }
        shared_ptr< QueryOp > runOp( QueryOp &op );
        template< class T >
        shared_ptr< T > runOp( T &op ) {
            return dynamic_pointer_cast< T >( runOp( static_cast< QueryOp& >( op ) ) );
        }
    private:
        struct RunnerSet {
            RunnerSet( QueryPlanSet &plans, QueryOp &op );
            shared_ptr< QueryOp > run();
            QueryOp &op_;
            QueryPlanSet &plans_;
            boost::barrier startBarrier_;
            bool firstDone_;            
        };
        struct Runner {
            Runner( QueryPlan &plan, RunnerSet &set, QueryOp &op ) :
            plan_( plan ),
            set_( set ),
            op_( op ) {}
            void operator()() {
                try {
                    set_.startBarrier_.wait();
                    QueryAborter aborter( set_.firstDone_ );
                    op_.run( plan_, aborter );
                    set_.firstDone_ = true;
                    op_.setComplete();
                } catch ( const QueryAborter::AbortException & ) {
                } catch ( const std::exception &e ) {
                    exceptionMessage_ = e.what();
                } catch ( ... ) {
                    exceptionMessage_ = "Caught unknown exception";
                }
            }
            QueryPlan &plan_;
            RunnerSet &set_;
            QueryOp &op_;
            string exceptionMessage_;
        };
        FieldBoundSet fbs_;
        typedef boost::shared_ptr< QueryPlan > PlanPtr;
        typedef vector< PlanPtr > PlanSet;
        PlanSet plans_;
    };
    
//    class QueryOptimizer {
//    public:
//        static QueryPlan getPlan(
//            const char *ns,
//            BSONObj* query,
//            BSONObj* order = 0,
//            BSONObj* hint = 0);
//    };

} // namespace mongo