[GitHub] [incubator-kvrocks] PragmaTwice commented on a diff in pull request #913: Customize prefix extractor for subkey

[GitBox <gi...@apache.org>]

PragmaTwice commented on code in PR #913:
URL: https://github.com/apache/incubator-kvrocks/pull/913#discussion_r978338376


##########
src/prefix_extractor.h:
##########
@@ -0,0 +1,54 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ *
+ */
+
+#pragma once
+
+#include <rocksdb/slice_transform.h>
+
+class SubkeyPrefixTransform : public rocksdb::SliceTransform {
+ private:
+  bool cluster_enabled_;
+  uint8_t prefix_base_len_;
+
+ public:
+  explicit SubkeyPrefixTransform(bool cluster_enabled) : cluster_enabled_(cluster_enabled) {
+    // Subkey format:
+    // 1(namespace_len) + N(namespace) + 2(slot_id) + 4(user_key_len) + N(user_key) + 8(version) + N(field) + ..
+    // If cluster_enabled is true, length of Subkey is not smaller than 15
+    // If cluster_enabled is false, length of Subkey is not smaller than 13
+    prefix_base_len_ = cluster_enabled ? 15 : 13;
+  }
+
+  const char* Name() const override { return "Kvrocks.SubkeyPrefix"; }
+
+  rocksdb::Slice Transform(const rocksdb::Slice& src) const override {
+    assert(InDomain(src));
+    size_t prefix_len = GetPrefixLen(src);
+    return rocksdb::Slice(src.data(), prefix_len);
+  }
+
+  bool InDomain(const rocksdb::Slice& src) const override {
+    return (src.size() >= prefix_base_len_);
+  }
+
+  size_t GetPrefixLen(const rocksdb::Slice& input) const;
+};
+
+extern const rocksdb::SliceTransform* NewSubkeyPrefixTransform(bool cluster_enabled);

Review Comment:
   I think, if you defined this function, you can move the definition of `class SubkeyPrefixTransform` to the source file `prefix_extractor.cc`. Or you can just remove this function.



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