HIVE-12679: Allow users to be able to specify an implementation of IMetaStoreClient via HiveConf

[moomindani]

What changes were proposed in this pull request?

This change makes it possible for users to choose an implementation of IMetaStoreClient via HiveConf, i.e. hive-site.xml.

This patch is to retry merging the patch of HIVE-12679.
I talked with Austin, the original contributor for this issue, and he said it is okay to submit this patch again.
https://issues.apache.org/jira/browse/HIVE-12679

Why are the changes needed?

Currently, in Hive the choice is hard coded to be SessionHiveMetaStoreClient in org.apache.hadoop.hive.ql.metadata.Hive.
There is no other direct reference to SessionHiveMetaStoreClient other than the hard coded class name in Hive.java and the QL component operates only on the IMetaStoreClient interface so the change would be minimal and it would be quite similar to how an implementation of RawStore is specified and loaded in hive-metastore. One use case this change would serve would be one where a user wishes to use an implementation of this interface without the dependency on the Thrift server.

Does this PR introduce any user-facing change?

Yes. User will be able to specify own implementation of IMetaStoreClient. (e.g. IMetaStoreClient for AWS Glue Data Catalog).

How was this patch tested?

Unit test and integration test with Glue Data Catalog client.

[sankarh]

I would like to bring up the comment from @thejasmn which sounds valid to me.
"Note that SessionHiveMetaStoreClient implements logic for temp tables, as they have a lifetime of a session. I am wondering if this config should determine which IMetaStoreClient impl is used by SessionHiveMetaStoreClient, instead of replacing SessionHiveMetaStoreClient itself.
Some changes to SessionHiveMetaStoreClient would be needed as well for that approach, for it to accept configured IMetaStoreClient."
Would you pls address this comment?

[moomindani]

@sankarh Thank you for the comment, I will try to address it.

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
Feel free to reach out on the dev@hive.apache.org list if the patch is in need of reviews.