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diff --git a/src/mongo/db/exec/ensure_sorted.h b/src/mongo/db/exec/ensure_sorted.h
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+/**
+ *    Copyright (C) 2015 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/exec/plan_stage.h"
+
+namespace mongo {
+
+/**
+ * Takes the output of its child and drops any results that are not in the sort order specified by
+ * 'pattern'. Thus, if the pattern is {a: -1} and the following documents are inputted:
+ *      {a: 9}, {a: 6}, {a: 8}, {a, 1}
+ * The third document will be dropped so that the output is:
+ *      {a: 9}, {a: 6}, {a, 1}
+ */
+class EnsureSortedStage final : public PlanStage {
+public:
+    EnsureSortedStage(OperationContext* opCtx, BSONObj pattern, WorkingSet* ws, PlanStage* child);
+
+    bool isEOF() final;
+    StageState work(WorkingSetID* out) final;
+
+    StageType stageType() const final {
+        return STAGE_ENSURE_SORTED;
+    }
+
+    std::unique_ptr<PlanStageStats> getStats() final;
+
+    const SpecificStats* getSpecificStats() const final;
+
+    static const char* kStageType;
+
+private:
+    /**
+     * Returns whether the result with the lhsSortKey should come before the result with the
+     * rhsSortKey in sort order.
+     */
+    bool isInOrder(const BSONObj& lhsSortKey, const BSONObj& rhsSortKey) const;
+
+    WorkingSet* _ws;
+
+    // The pattern that we're sorting by.
+    BSONObj _pattern;
+
+    // The sort key of the previous result.
+    BSONObj _prevSortKey;
+
+    EnsureSortedStats _specificStats;
+};
+
+}  // namespace mongo