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From "Gunther Hagleitner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6518) Add a GC canary to the VectorGroupByOperator to flush whenever a GC is triggered
Date Thu, 27 Feb 2014 23:38:21 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13915212#comment-13915212
] 

Gunther Hagleitner commented on HIVE-6518:
------------------------------------------

I like it. Sounds like this will allow you to be more aggressive with caching/flushing params,
while having a trigger that will flush out stuff when necessary.

+1 (assuming tests pass)

> Add a GC canary to the VectorGroupByOperator to flush whenever a GC is triggered
> --------------------------------------------------------------------------------
>
>                 Key: HIVE-6518
>                 URL: https://issues.apache.org/jira/browse/HIVE-6518
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.13.0
>            Reporter: Gopal V
>            Assignee: Gopal V
>            Priority: Minor
>         Attachments: HIVE-6518.1-tez.patch
>
>
> The current VectorGroupByOperator implementation flushes the in-memory hashes when the
maximum entries or fraction of memory is hit.
> This works for most cases, but there are some corner cases where we hit GC ovehead limits
or heap size limits before either of those conditions are reached due to the rest of the pipeline.
> This patch adds a SoftReference as a GC canary. If the soft reference is dead, then a
full GC pass happened sometime in the near past & the aggregation hashtables should be
flushed immediately before another full GC is triggered.



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