SERVER-14098 add CountStage

1 files changed, 132 insertions, 0 deletions

diff --git a/src/mongo/db/exec/count_scan.h b/src/mongo/db/exec/count_scan.h
new file mode 100644
index 00000000000..70ebb289dd5
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+++ b/src/mongo/db/exec/count_scan.h
@@ -0,0 +1,132 @@
+/**
+ *    Copyright (C) 2014 MongoDB 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 "mongo/db/exec/plan_stage.h"
+#include "mongo/db/diskloc.h"
+#include "mongo/db/index/btree_index_cursor.h"
+#include "mongo/db/index/index_access_method.h"
+#include "mongo/db/jsobj.h"
+#include "mongo/db/matcher/expression.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/platform/unordered_set.h"
+
+namespace mongo {
+
+    class IndexAccessMethod;
+    class IndexDescriptor;
+    class WorkingSet;
+
+    struct CountScanParams {
+        CountScanParams() : descriptor(NULL) { }
+
+        // What index are we traversing?
+        const IndexDescriptor* descriptor;
+
+        BSONObj startKey;
+        bool startKeyInclusive;
+
+        BSONObj endKey;
+        bool endKeyInclusive;
+    };
+
+    /**
+     * Used by the count command.  Scans an index from a start key to an end key.  Does not create
+     * any WorkingSetMember(s) for any of the data, instead returning ADVANCED to indicate to the
+     * caller that another result should be counted.
+     *
+     * Only created through the getExecutorCount path, as count is the only operation that doesn't
+     * care about its data.
+     */
+    class CountScan : public PlanStage {
+    public:
+        CountScan(OperationContext* txn, const CountScanParams& params, WorkingSet* workingSet);
+        virtual ~CountScan() { }
+
+        virtual StageState work(WorkingSetID* out);
+        virtual bool isEOF();
+        virtual void saveState();
+        virtual void restoreState(OperationContext* opCtx);
+        virtual void invalidate(const DiskLoc& dl, InvalidationType type);
+
+        virtual std::vector<PlanStage*> getChildren() const;
+
+        virtual StageType stageType() const { return STAGE_COUNT_SCAN; }
+
+        virtual PlanStageStats* getStats();
+
+        virtual const CommonStats* getCommonStats();
+
+        virtual const SpecificStats* getSpecificStats();
+
+        static const char* kStageType;
+
+    private:
+        /**
+         * Initialize the underlying IndexCursor
+         */
+        void initIndexCursor();
+
+        /**
+         * See if we've hit the end yet.
+         */
+        void checkEnd();
+
+        // transactional context for read locks. Not owned by us
+        OperationContext* _txn;
+
+        // The WorkingSet we annotate with results.  Not owned by us.
+        WorkingSet* _workingSet;
+
+        // Index access.  Both pointers below are owned by Collection -> IndexCatalog.
+        const IndexDescriptor* _descriptor;
+        const IndexAccessMethod* _iam;
+
+        // Our start cursor is _btreeCursor.
+        boost::scoped_ptr<BtreeIndexCursor> _btreeCursor;
+
+        // Our end marker.
+        boost::scoped_ptr<BtreeIndexCursor> _endCursor;
+
+        // Could our index have duplicates?  If so, we use _returned to dedup.
+        unordered_set<DiskLoc, DiskLoc::Hasher> _returned;
+
+        CountScanParams _params;
+
+        bool _hitEnd;
+
+        bool _shouldDedup;
+
+        CommonStats _commonStats;
+        CountScanStats _specificStats;
+    };
+
+}  // namespace mongo