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diff --git a/storage/rocksdb/rdb_comparator.h b/storage/rocksdb/rdb_comparator.h
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+/*
+   Copyright (c) 2012,2015 Monty Program Ab
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1301 USA */
+#pragma once
+
+/* C++ system header files */
+#include <string>
+
+/* MySQL includes */
+#include "./m_ctype.h"
+
+/* RocksDB header files */
+#include "rocksdb/comparator.h"
+
+/* MyRocks header files */
+#include "./rdb_utils.h"
+
+namespace myrocks {
+
+/*
+  The keys are in form: {index_number} {mem-comparable-key}
+
+  (todo: knowledge about this format is shared between this class and
+   Rdb_key_def)
+*/
+class Rdb_pk_comparator : public rocksdb::Comparator {
+ public:
+  Rdb_pk_comparator(const Rdb_pk_comparator &) = delete;
+  Rdb_pk_comparator &operator=(const Rdb_pk_comparator &) = delete;
+  Rdb_pk_comparator() = default;
+
+  // extracting from rocksdb::BytewiseComparator()->Compare() for optimization
+  int Compare(const rocksdb::Slice &a, const rocksdb::Slice &b) const override {
+    return a.compare(b);
+  }
+
+  const char *Name() const override { return "RocksDB_SE_v3.10"; }
+
+  // TODO: advanced funcs:
+  // - FindShortestSeparator
+  // - FindShortSuccessor
+
+  // for now, do-nothing implementations:
+  void FindShortestSeparator(std::string *start,
+                             const rocksdb::Slice &limit) const override {
+    rocksdb::BytewiseComparator()->FindShortestSeparator(start, limit);
+  }
+  void FindShortSuccessor(std::string *key) const override {
+    rocksdb::BytewiseComparator()->FindShortSuccessor(key);
+  }
+};
+
+class Rdb_rev_comparator : public rocksdb::Comparator {
+ public:
+  Rdb_rev_comparator(const Rdb_rev_comparator &) = delete;
+  Rdb_rev_comparator &operator=(const Rdb_rev_comparator &) = delete;
+  Rdb_rev_comparator() = default;
+
+  // extracting from rocksdb::BytewiseComparator()->Compare() for optimization
+  int Compare(const rocksdb::Slice &a, const rocksdb::Slice &b) const override {
+    return -a.compare(b);
+  }
+  const char *Name() const override { return "rev:RocksDB_SE_v3.10"; }
+  void FindShortestSeparator(std::string *start,
+                             const rocksdb::Slice &limit) const override {
+    rocksdb::ReverseBytewiseComparator()->FindShortestSeparator(start, limit);
+  }
+  void FindShortSuccessor(std::string *key) const override {
+    rocksdb::ReverseBytewiseComparator()->FindShortSuccessor(key);
+  }
+};
+
+}  // namespace myrocks