SERVER-12113 keep mutated docs in query results when it's sane to

1 files changed, 82 insertions, 0 deletions

diff --git a/src/mongo/db/exec/keep_mutations.h b/src/mongo/db/exec/keep_mutations.h
new file mode 100644
index 00000000000..66fd1516814
--- /dev/null
+++ b/src/mongo/db/exec/keep_mutations.h
@@ -0,0 +1,82 @@
+/**
+ *    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 "mongo/db/diskloc.h"
+#include "mongo/db/jsobj.h"
+#include "mongo/db/exec/plan_stage.h"
+#include "mongo/db/matcher/expression.h"
+
+namespace mongo {
+
+    /**
+     * KeepMutationsStage passes all of its child's data through until the child is EOF.
+     * It then returns all flagged elements in the WorkingSet that pass the stage's filter.
+     *
+     * This stage is used to merge results that are invalidated mid-query back into the query
+     * results when possible.  The query planner is responsible for determining when it's valid to
+     * merge these results.
+     */
+    class KeepMutationsStage : public PlanStage {
+    public:
+        KeepMutationsStage(const MatchExpression* filter, WorkingSet* ws, PlanStage* child);
+        virtual ~KeepMutationsStage();
+
+        virtual bool isEOF();
+        virtual StageState work(WorkingSetID* out);
+
+        virtual void prepareToYield();
+        virtual void recoverFromYield();
+        virtual void invalidate(const DiskLoc& dl, InvalidationType type);
+
+        virtual PlanStageStats* getStats();
+
+    private:
+        // Not owned here.
+        WorkingSet* _workingSet;
+
+        scoped_ptr<PlanStage> _child;
+
+        // Not owned here.  Should be the full query expression tree.
+        const MatchExpression* _filter;
+
+        // We read from our child...
+        bool _doneReadingChild;
+
+        // ...until it's out of results, at which point we put any flagged results back in the query
+        // stream.
+        bool _doneReturningFlagged;
+
+        // Stats
+        CommonStats _commonStats;
+
+        unordered_set<WorkingSetID>::const_iterator _flaggedIterator;
+    };
+
+}  // namespace mongo