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https://issues.apache.org/jira/browse/SPARK-22394?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16224028#comment-16224028
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Zhenhua Wang commented on SPARK-22394:
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[~cloud_fan] [~smilegator] [~rxin] Do I understand it correctly, or do I miss
something?
> Redundant synchronization for metastore access
> ----------------------------------------------
>
> Key: SPARK-22394
> URL: https://issues.apache.org/jira/browse/SPARK-22394
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.3.0
> Reporter: Zhenhua Wang
>
> Before Spark 2.x, synchronization for metastore access was protected at
> [line229 in ClientWrapper
> |https://github.com/apache/spark/blob/branch-1.6/sql/hive/src/main/scala/org/apache/spark/sql/hive/client/ClientWrapper.scala#L229]
> (now it's at [line203 in HiveClientWrapper
> |https://github.com/apache/spark/blob/master/sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala#L203]).
> After Spark 2.x, HiveExternalCatalog was introduced by
> [SPARK-13080|https://github.com/apache/spark/pull/11293], where an extra
> level of synchronization was added at
> [line95|https://github.com/apache/spark/blob/master/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveExternalCatalog.scala#L95].
> That is, now we have two levels of synchronization: one is
> HiveExternalCatalog and the other is IsolatedClientLoader in HiveClientImpl.
> But since both HiveExternalCatalog and IsolatedClientLoader are shared among
> all spark sessions, I think the extra level of synchronization in
> HiveExternalCatalog is redundant, thus can be removed.
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