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Date: Mon, 3 May 2010 16:53:58 -0400 (EDT)
From: "Namit Jain (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
Subject: [jira] Assigned: (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:all-tabpanel ]

Namit Jain reassigned HIVE-1293:
--------------------------------

    Assignee: Namit Jain

> 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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