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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1293) Concurrency Model for Hive
Date Mon, 23 Aug 2010 20:09:20 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901571#action_12901571
] 

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

You must have set: hive.supports.concurrency to true.

The only case that you are trying to optimize is: 'show tables', 'desc ..' etc.
The problem is that 'show Locks' also comes under the same category - no locks need to be
acquired.
I didnt want to special case 'show Locks'

> Concurrency 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
>             Fix For: 0.7.0
>
>         Attachments: hive.1293.1.patch, hive.1293.2.patch, hive.1293.3.patch, hive.1293.4.patch,
hive.1293.5.patch, hive.1293.6.patch, hive.1293.7.patch, hive.1293.8.patch, hive_leases.txt
>
>
> 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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