Github user sihuazhou commented on a diff in the pull request:
https://github.com/apache/flink/pull/6159#discussion_r195299958
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/AbstractKeyGroupPartitioner.java
---
@@ -0,0 +1,227 @@
+/*
+ * 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.
+ */
+
+package org.apache.flink.runtime.state;
+
+import org.apache.flink.util.Preconditions;
+
+import javax.annotation.Nonnegative;
+import javax.annotation.Nonnull;
+
+/**
+ * Abstract class that contains the base algorithm for partitioning data
into key-groups. This algorithm currently works
+ * with two array (input, output) for optimal algorithmic complexity.
Notice that this could also be implemented over a
+ * single array, using some cuckoo-hashing-style element replacement. This
would have worse algorithmic complexity but
+ * better space efficiency. We currently prefer the trade-off in favor of
better algorithmic complexity.
+ */
--- End diff --
Maybe we could add a param annotation for `T`.
---
