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From "Olga Natkovich (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-636) PERFORMANCE: Use lightweight bag implementations which do not register with SpillableMemoryManager with Combiner
Date Tue, 27 Jan 2009 20:03:01 GMT

    [ https://issues.apache.org/jira/browse/PIG-636?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12667778#action_12667778
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Olga Natkovich commented on PIG-636:
------------------------------------

+1 on the patch. The only minor thing that I saw that needs to be changes is size of a single
tuple bag should be changed to 1 rather than 0.

> PERFORMANCE: Use lightweight bag implementations which do not register with SpillableMemoryManager
with Combiner
> ----------------------------------------------------------------------------------------------------------------
>
>                 Key: PIG-636
>                 URL: https://issues.apache.org/jira/browse/PIG-636
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: types_branch
>            Reporter: Pradeep Kamath
>            Assignee: Pradeep Kamath
>             Fix For: types_branch
>
>         Attachments: PIG-636.patch
>
>
> Currently whenever Combiner is used in pig, in the map, the POPrecombinerLocalRearrange
operator puts the single "value" tuple corresponding to a key into a DataBag and passes this
to the foreach which is being combined. This will generate as many bags as there are input
records. These bags all will have a single tuple and hence are small and should not need to
be spilt to disk. However since the bags are created through the BagFactory mechanism, each
bag creation is registered with the SpillableMemoryManager and a weak reference to the bag
is stored in a linked list. This linked list grows really big over time causing unnecessary
Garbage collection runs. This can be avoided by having a simple lightweight implementation
of the DataBag interface to store the single tuple in a bag. Also these SingleTupleBags should
be created without registering with the spillableMemoryManager. Likewise the bags created
in POCombinePackage are supposed to fit in Memory and not spill. Again a NonSpillableDataBag
implementation of DataBag interface which does not register with the SpillableMemoryManager
would help.

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