spdb memtable: add a new hash-based memtable

This memtable supports concurrent readers and writers and provides much
better results for insertions and point selections than the skip list
memtable, while maintaining more tolerable iteration performance than the
built-in RocksDB hash-based memtable.

memtable/stl_wrappers.h

@@ -27,6 +27,9 @@ struct Compare : private Base {
   inline bool operator()(const char* a, const char* b) const {
     return compare_(a, b) < 0;
   }
+  inline bool operator()(const char* a, const Slice& b) const {
+    return compare_(a, b) < 0;
+  }
 };
 
 }

plugin/speedb/CMakeLists.txt

@@ -0,0 +1,18 @@
+# Copyright (C) 2022 Speedb Ltd. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set(speedb_SOURCES
+      speedb_registry.cc
+      memtable/hash_spd_rep.cc)
+
+set(speedb_FUNC register_SpeedbPlugins)