Github user yhuai commented on the pull request: https://github.com/apache/spark/pull/13236#issuecomment-221050299 @rdblue Thank you for looking at this! The reason that I added the flag to disable sharing Hadoop classes is that hadoops used by Spark and metastore client may not be binary compatible (e.g. hadoop 2 used by spark and hadoop 1 used by the metastore client). For HiveClientImpl, it is a wrapper of a Hive's metastore client. As long as we can propagate user set configurations to its internal HiveConf (to make it talk the metastore correctly), it is fine. Regarding the classloader, we actually do not use the classloader originally associated with the Hadoop Configuration and we always explicitly set the classloader associated with the HiveConf created inside HiveClientImpl. Regarding Configuration.addDefaultResource, before 2.0, we did not pass Hadoop Configuration to HiveClientImpl (it was called ClientWrapper in Spark 1.6). Since we were not relying on Configuration.addDefaultResource, using a Map should not change anything. btw, I am fine to change the default value of the flag to true (sharing hadoop classes) if you think it represents common use cases.
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