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diff --git a/src/mongo/db/exec/subplan.h b/src/mongo/db/exec/subplan.h
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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 <boost/scoped_ptr.hpp>
+#include <string>
+#include <queue>
+
+#include "mongo/base/status.h"
+#include "mongo/db/diskloc.h"
+#include "mongo/db/exec/plan_stage.h"
+#include "mongo/db/query/query_planner_params.h"
+#include "mongo/db/query/query_solution.h"
+
+namespace mongo {
+
+    /**
+     * The SubplanStage is used for rooted $or queries. It plans each clause of the $or
+     * individually, and then creates an overall query plan based on the winning plan from
+     * each clause.
+     *
+     * Uses the MultiPlanStage in order to rank plans for the individual clauses.
+     */
+    class SubplanStage : public PlanStage {
+    public:
+        /**
+         * Used to create SubplanStage instances. The caller owns the instance
+         * returned through 'out'.
+         *
+         * 'out' is valid only if an OK status is returned.
+         */
+        static Status make(Collection* collection,
+                           WorkingSet* ws,
+                           const QueryPlannerParams& params,
+                           CanonicalQuery* cq,
+                           SubplanStage** out);
+
+        virtual ~SubplanStage();
+
+        static bool canUseSubplanning(const CanonicalQuery& query);
+
+        virtual bool isEOF();
+        virtual StageState work(WorkingSetID* out);
+
+        virtual void prepareToYield();
+        virtual void recoverFromYield();
+        virtual void invalidate(const DiskLoc& dl, InvalidationType type);
+
+        virtual std::vector<PlanStage*> getChildren() const;
+
+        virtual StageType stageType() const { return STAGE_SUBPLAN; }
+
+        PlanStageStats* getStats();
+
+        static const char* kStageType;
+
+        /**
+         * Plan each branch of the $or independently, and store the resulting
+         * lists of query solutions in '_solutions'.
+         *
+         * Called from SubplanStage::make so that construction of the subplan stage
+         * fails immediately, rather than returning a plan executor and subsequently
+         * through getNext(...).
+         */
+        Status planSubqueries();
+
+    private:
+        SubplanStage(Collection* collection,
+                     WorkingSet* ws,
+                     const QueryPlannerParams& params,
+                     CanonicalQuery* cq);
+
+        bool runSubplans();
+
+        enum SubplanningState {
+            PLANNING,
+            RUNNING,
+        };
+
+        SubplanningState _state;
+
+        Collection* _collection;
+
+        // Not owned here.
+        WorkingSet* _ws;
+
+        QueryPlannerParams _plannerParams;
+
+        // Not owned here.
+        CanonicalQuery* _query;
+
+        bool _killed;
+
+        boost::scoped_ptr<PlanStage> _child;
+
+        // We do the subquery planning up front, and keep the resulting
+        // query solutions here. Lists of query solutions are dequeued
+        // and ownership is transferred to the underlying runners one
+        // at a time.
+        std::queue< std::vector<QuerySolution*> > _solutions;
+
+        // Holds the canonicalized subqueries. Ownership is transferred
+        // to the underlying runners one at a time.
+        std::queue<CanonicalQuery*> _cqs;
+
+        // We need this to extract cache-friendly index data from the index assignments.
+        map<BSONObj, size_t> _indexMap;
+
+        CommonStats _commonStats;
+    };
+
+}  // namespace mongo