SERVER-14097 SERVER-14098 execution-level explain for .find() and .count()

The explain implementation for .find() and .count() is feature complete. To use
the .find() implementation, set the enableNewExplain setParameter to true.

Count operations are explained through the new explain command, e.g.
db.runCommand({explain: {count: "coll", query: {foo: "bar"}}}).

1 files changed, 138 insertions, 0 deletions

diff --git a/src/mongo/db/exec/subplan.h b/src/mongo/db/exec/subplan.h
new file mode 100644
index 00000000000..1fb6c698523
--- /dev/null
+++ b/src/mongo/db/exec/subplan.h
@@ -0,0 +1,138 @@
+/**
+ *    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