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diff --git a/src/mongo/db/transaction_reaper.h b/src/mongo/db/transaction_reaper.h
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+/**
+ * Copyright (C) 2017 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 <memory>
+
+namespace mongo {
+
+class ServiceContext;
+class SessionsCollection;
+class OperationContext;
+
+/**
+ * TransactionReaper is responsible for scanning the transaction table, checking if sessions are
+ * still alive and deleting the transaction records if their sessions have expired.
+ */
+class TransactionReaper {
+public:
+    enum class Type {
+        kReplicaSet,
+        kSharded,
+    };
+
+    virtual ~TransactionReaper() = 0;
+
+    virtual void reap(OperationContext* OperationContext) = 0;
+
+    /**
+     * The implementation of the sessions collections is different in replica sets versus sharded
+     * clusters, so we have a factory to pick the right impl.
+     */
+    static std::unique_ptr<TransactionReaper> make(Type type,
+                                                   std::shared_ptr<SessionsCollection> collection);
+};
+
+}  // namespace mongo