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From "John Sichi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1293) Concurreny Model for Hive
Date Wed, 05 May 2010 08:08:03 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12864227#action_12864227
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John Sichi commented on HIVE-1293:
----------------------------------

Just to clarify, when you say this:

"The lock modes are hierarchical in nature - if 'S' lock is acquired on T, implicitly 'S'
lock is acquired on all partitions of T."

it only applies when no partition is specified, so for

select .. T1 partition P1 => S on T1, T1.P1  

we only S-lock T1.P1 (not all the other partitions of T), right?


> Concurreny Model for Hive
> -------------------------
>
>                 Key: HIVE-1293
>                 URL: https://issues.apache.org/jira/browse/HIVE-1293
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Namit Jain
>
> Concurrency model for Hive:
> Currently, hive does not provide a good concurrency model. The only guanrantee provided
in case of concurrent readers and writers is that
> reader will not see partial data from the old version (before the write) and partial
data from the new version (after the write).
> This has come across as a big problem, specially for background processes performing
maintenance operations.
> The following possible solutions come to mind.
> 1. Locks: Acquire read/write locks - they can be acquired at the beginning of the query
or the write locks can be delayed till move
> task (when the directory is actually moved). Care needs to be taken for deadlocks.
> 2. Versioning: The writer can create a new version if the current version is being read.
Note that, it is not equivalent to snapshots,
> the old version can only be accessed by the current readers, and will be deleted when
all of them have finished.
> Comments.

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