1 files changed, 77 insertions, 0 deletions
diff --git a/src/rocksdb/utilities/merge_operators/max.cc b/src/rocksdb/utilities/merge_operators/max.cc
new file mode 100644
index 000000000..2270c1f03
--- /dev/null
+++ b/src/rocksdb/utilities/merge_operators/max.cc
@@ -0,0 +1,77 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+
+#include <memory>
+
+#include "rocksdb/merge_operator.h"
+#include "rocksdb/slice.h"
+#include "utilities/merge_operators.h"
+
+using ROCKSDB_NAMESPACE::Logger;
+using ROCKSDB_NAMESPACE::MergeOperator;
+using ROCKSDB_NAMESPACE::Slice;
+
+namespace {  // anonymous namespace
+
+// Merge operator that picks the maximum operand, Comparison is based on
+// Slice::compare
+class MaxOperator : public MergeOperator {
+ public:
+  bool FullMergeV2(const MergeOperationInput& merge_in,
+                   MergeOperationOutput* merge_out) const override {
+    Slice& max = merge_out->existing_operand;
+    if (merge_in.existing_value) {
+      max = Slice(merge_in.existing_value->data(),
+                  merge_in.existing_value->size());
+    } else if (max.data() == nullptr) {
+      max = Slice();
+    }
+
+    for (const auto& op : merge_in.operand_list) {
+      if (max.compare(op) < 0) {
+        max = op;
+      }
+    }
+
+    return true;
+  }
+
+  bool PartialMerge(const Slice& /*key*/, const Slice& left_operand,
+                    const Slice& right_operand, std::string* new_value,
+                    Logger* /*logger*/) const override {
+    if (left_operand.compare(right_operand) >= 0) {
+      new_value->assign(left_operand.data(), left_operand.size());
+    } else {
+      new_value->assign(right_operand.data(), right_operand.size());
+    }
+    return true;
+  }
+
+  bool PartialMergeMulti(const Slice& /*key*/,
+                         const std::deque<Slice>& operand_list,
+                         std::string* new_value,
+                         Logger* /*logger*/) const override {
+    Slice max;
+    for (const auto& operand : operand_list) {
+      if (max.compare(operand) < 0) {
+        max = operand;
+      }
+    }
+
+    new_value->assign(max.data(), max.size());
+    return true;
+  }
+
+  const char* Name() const override { return "MaxOperator"; }
+};
+
+}  // end of anonymous namespace
+
+namespace ROCKSDB_NAMESPACE {
+
+std::shared_ptr<MergeOperator> MergeOperators::CreateMaxOperator() {
+  return std::make_shared<MaxOperator>();
+}
+}  // namespace ROCKSDB_NAMESPACE