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From "Chaoyu Tang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-8136) Reduce table locking
Date Thu, 16 Apr 2015 18:47:01 GMT

    [ https://issues.apache.org/jira/browse/HIVE-8136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14498498#comment-14498498
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Chaoyu Tang commented on HIVE-8136:
-----------------------------------

[~Ferd] I have a question, when Hive processes a query, it needs fetch Table/Partition/Serde
metadata from HMS, is this metadata cached at HMS client side (as Table/Partition) or to be
retrieved from HMS each time it is needed, no matter the metadata is cached at HMS (as JDO
entity object)? If the first one is the case, it is easer and I think the change should be
fine. 
Otherwise, I think we should be more conservative and might even need add DDL_EXCLUSIVE on
anything which may affect other query behaviors (e.g. ADDPROP etc). For example, querying
data for an Avro or HBase backed tables, the Avro schema url/literal or HBase column mapping
is specified as a property. Can we guarantee that Hive only need access these data once or
all the metadata has been cached at its HMS client?

> Reduce table locking
> --------------------
>
>                 Key: HIVE-8136
>                 URL: https://issues.apache.org/jira/browse/HIVE-8136
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Brock Noland
>            Assignee: Ferdinand Xu
>         Attachments: HIVE-8136.1.patch, HIVE-8136.patch
>
>
> When using ZK for concurrency control, some statements require an exclusive table lock
when they are atomic. Such as setting a tables location.
> This JIRA is to analyze the scope of statements like ALTER TABLE and see if we can reduce
the locking required.



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