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https://issues.apache.org/jira/browse/HIVE-21115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16740861#comment-16740861
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Oliver Draese commented on HIVE-21115:
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One thing that might be worth considering here is the requirement to include
DDL in general transaction management. If we add support for multiple
statements within a single transaction and allow DDL statements to be part of
these transactions, then we probably have the WriterID of the transaction
already as a version identifier. The WriterID could also be used to detect
optimistic locking conflicts and the WriterID column could then also be used as
JDO version field.
> 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
> Priority: Major
>
> 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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