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From "John Sichi (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HIVE-1557) increase concurrency
Date Thu, 19 Aug 2010 21:00:17 GMT

     [ https://issues.apache.org/jira/browse/HIVE-1557?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

John Sichi updated HIVE-1557:

        Fix Version/s: 0.7.0
    Affects Version/s: 0.7.0

> increase concurrency
> --------------------
>                 Key: HIVE-1557
>                 URL: https://issues.apache.org/jira/browse/HIVE-1557
>             Project: Hadoop Hive
>          Issue Type: Improvement
>          Components: Query Processor
>    Affects Versions: 0.7.0
>            Reporter: Namit Jain
>             Fix For: 0.7.0
> Copying Joy's comment from https://issues.apache.org/jira/browse/HIVE-1293
> a little bummed that locks need to be held for entire query execution. that could mean
a writer blocking readers for hours.
> hive's query plans seem to be of two distinct stages:
> 1. read a bunch of stuff, compute intermediate/final data
> 2. move final data into output locations
> ie. - a single query never reads what it writes (into a final output location). even
if #1 and #2 are mingled today - they can easily be put in order.
> in that sense - we only need to get shared locks for all read entities involved in #1
to begin with. once phase #1 is done, we can drop all the read locks and get the exclusive
locks for all the write entities in #2, perform #2 and quit. that way exclusive locks are
held for a very short duration. i think this scheme is similarly deadlock free (now there
are two independent lock acquire/release phases - and each of them can lock stuff in lex.

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