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https://issues.apache.org/jira/browse/HIVE-21115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16750280#comment-16750280
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Bharathkrishna Guruvayoor Murali commented on HIVE-21115:
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Hi Alan, sure we can proceed after discussing and getting the consensus. The
main idea of putting this patch is for everyone to get an idea of how we are
currently thinking of implementing this and to see if any unexpected tests fail
to detect early if there are any problems with the approach.
Updating the versions via datanucleus has a problem that the updated version
number is not reflected in the MetaStoreConf notifications for transactional
listeners because the notifications are issued before commitTransaction().
Hence, the logic in the prototype patch attached involves select..for update on
the respective table/partition row to update version. As I mentioned, let's go
ahead and put more thoughts into this, and the patch just serves to give more
clarity on the idea.
> Add support for object versions in metastore
> --------------------------------------------
>
> Key: HIVE-21115
> URL: https://issues.apache.org/jira/browse/HIVE-21115
> Project: Hive
> Issue Type: Improvement
> Reporter: Vihang Karajgaonkar
> Assignee: Bharathkrishna Guruvayoor Murali
> Priority: Major
> Attachments: HIVE-21115.1.patch, HIVE-21115.2.patch
>
>
> Currently, metastore objects are identified uniquely by their names (eg.
> catName, dbName and tblName for a table is unique). Once a table or partition
> is created it could be altered in many ways. There is no good way currently
> to identify the version of the object once it is altered. For example,
> suppose there are two clients (Hive and Impala) using the same metastore.
> Once some alter operations are performed by a client, another client which
> wants to do a alter operation has no good way to know if the object which it
> has is the same as the one stored in metastore. Metastore updates the
> {{transient_lastDdlTime}} every time there is a DDL operation on the object.
> However, this value cannot be relied for all the clients since after
> HIVE-1768 metastore updates the value only when it is not set in the
> parameters. It is possible that a client which alters the object state, does
> not remove the {{transient_lastDdlTime}} and metastore will not update it.
> Secondly, if there is a clock skew between multiple HMS instances when HMS-HA
> is configured, time values cannot be relied on to find out the sequence of
> alter operations on a given object.
> This JIRA propose to use JDO versioning support by Datanucleus
> http://www.datanucleus.org/products/accessplatform_4_2/jdo/versioning.html to
> generate a incrementing sequence number every time a object is altered. The
> value of this object can be set as one of the values in the parameters. The
> advantage of using Datanucleus the versioning can be done across HMS
> instances as part of the database transaction and it should work for all the
> supported databases.
> In theory such a version can be used to detect if the client is presenting a
> object which is "stale" when issuing a alter request. Metastore can choose to
> reject such a alter request since the client may be caching a old version of
> the object and any alter operation on such stale object can potentially
> overwrite previous operations. However, this is can be done in a separate
> JIRA.
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