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https://issues.apache.org/jira/browse/PARQUET-1951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17258542#comment-17258542
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ASF GitHub Bot commented on PARQUET-1951:
-----------------------------------------
satishkotha commented on a change in pull request #847:
URL: https://github.com/apache/parquet-mr/pull/847#discussion_r551598592
##########
File path:
parquet-hadoop/src/main/java/org/apache/parquet/hadoop/metadata/KeyValueMetadataMergeStrategy.java
##########
@@ -0,0 +1,44 @@
+/*
+ * 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.parquet.hadoop.metadata;
+
+import org.apache.parquet.schema.MessageType;
+
+import java.io.Serializable;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Objects;
+import java.util.Set;
+
+import static java.util.Collections.unmodifiableMap;
+
+/**
+ * Strategy to merge metadata. Possible implementations:
+ * 1) Expect metadata to be exactly identical. Otherwise throw error (this is
the default strategy implementation)
+ * 2) Custom strategy to merge metadata if the values are not identical.
Example: concatenate values.
+ */
+public interface KeyValueMetadataMergeStrategy extends Serializable {
+ /**
+ * @param keyValueMetaData the merged app specific metadata
+ *
+ * @throws NullPointerException if keyValueMetaData is {@code null}
+ */
+ Map<String, String> merge(Map<String, Set<String>> keyValueMetaData);
Review comment:
GlobalMetadata uses Map<String, Set \<String\>>
https://github.com/apache/parquet-mr/blob/master/parquet-hadoop/src/main/java/org/apache/parquet/hadoop/metadata/GlobalMetaData.java#L41.
So merge method takes in same argument.
Do you think it makes sense to change GlobalMetadata to track items in
List<String>? I'm not sure if it would be backward compatible and if there are
use cases expecting this to be Set.
Without changing GlobalMetadata#keyValueMetaData, it may not be useful to
change this interface. Let me know what you think.
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> Allow different strategies to combine key values when merging parquet files
> ---------------------------------------------------------------------------
>
> Key: PARQUET-1951
> URL: https://issues.apache.org/jira/browse/PARQUET-1951
> Project: Parquet
> Issue Type: Improvement
> Reporter: satish
> Priority: Minor
>
> I work on Apache Hudi project. We store some additional metadata in parquet
> files (key range in the file, for example). So the metadata is different in
> different parquet files that we want to merge these files.
> Here is what I'm thinking:
> 1) Merge command takes additional command line option: --strategy
> <StrategyClassName>.
> 2) We introduce new strategy class in parquet-hadoop to keep the same
> behavior as today.
> We can extend that class and provide our custom implementation.
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