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From "Gopal V (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-13809) Hybrid Grace Hash Join memory usage estimation didn't take into account the bloom filter size
Date Mon, 20 Jun 2016 22:07:57 GMT

    [ https://issues.apache.org/jira/browse/HIVE-13809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15340503#comment-15340503
] 

Gopal V commented on HIVE-13809:
--------------------------------

LGTM - +1.

The bloom filter sizing needs a revisit, since this is pre-allocated based on estimates, not
on real row-counts - allowing more false positives at higher cardinalities, to keep the memory
utilization under check.

> Hybrid Grace Hash Join memory usage estimation didn't take into account the bloom filter
size
> ---------------------------------------------------------------------------------------------
>
>                 Key: HIVE-13809
>                 URL: https://issues.apache.org/jira/browse/HIVE-13809
>             Project: Hive
>          Issue Type: Bug
>          Components: Hive
>    Affects Versions: 2.0.0, 2.1.0
>            Reporter: Wei Zheng
>            Assignee: Wei Zheng
>         Attachments: HIVE-13809.1.patch
>
>
> Memory estimation is important during hash table loading, because we need to make the
decision of whether to load the next hash partition in memory or spill it. If the assumption
is there's enough memory but it turns out not the case, we will run into OOM problem.
> Currently hybrid grace hash join memory usage estimation didn't take into account the
bloom filter size. In large test cases (TB scale) the bloom filter grows as big as hundreds
of MB, big enough to cause estimation error.
> The solution is to count in the bloom filter size into memory estimation.
> Another issue this patch will fix is possible NPE due to object cache reuse during hybrid
grace hash join.



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