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Date: Wed, 5 May 2010 17:36:05 -0400 (EDT)
From: "Namit Jain (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
Subject: [jira] Commented: (HIVE-1293) Concurreny Model for Hive
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    [ https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12864520#action_12864520 ] 

Namit Jain commented on HIVE-1293:
----------------------------------

Forgot to add before, I was thinking of a one-to-map mapping between a table and a znode.

For eg: if there are 2 tables: T1 and T2 with partitions T1.p=1, T1.p=2 and T2.p1=1,p2=1 and T2.p1=1,p2=2 respectively, the corresponding znodes will be:


T1  
    -> p=1
    -> p=2
T2
    -> p1=1
                 ->p2=1
                 ->p2=2


> 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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