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https://issues.apache.org/jira/browse/HIVE-1557?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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John Sichi updated HIVE-1557:
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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. order).
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