Github user jparkie commented on a diff in the pull request:
https://github.com/apache/flink/pull/4652#discussion_r140826158
--- Diff:
flink-libraries/flink-table/src/main/java/org/apache/flink/table/runtime/functions/aggfunctions/cardinality/MurmurHash.java
---
@@ -0,0 +1,247 @@
+/*
+ * 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.table.runtime.functions.aggfunctions.cardinality;
+
+/**
+ * This is a very fast, non-cryptographic hash suitable for general
hash-based
+ * lookup. See http://murmurhash.googlepages.com/ for more details.
+ * <p/>
+ */
+public class MurmurHash {
--- End diff --
What was the decision in choosing MurmurHash2 (in
https://github.com/tnm/murmurhash-java) versus MurmurHash3 (in
https://github.com/google/guava/blob/master/guava/src/com/google/common/hash/Murmur3_32HashFunction.java)?
If I recall correctly, MurmurHash3 is more collision resistant and slightly
faster than MurmurHash2.
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