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https://issues.apache.org/jira/browse/TEZ-4069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16842417#comment-16842417
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Oliver Draese commented on TEZ-4069:
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{color:#FF0000}>> The patch doesn't appear to include any new or modified
tests. Please justify why no new tests are needed for this patch. Also please
list what manual steps were performed to verify this patch.{color}
Existing TestGroupedSplits covers the changed code path. It runs successfully.
> Avoid repeated computation of preferred locations in split grouping.
> --------------------------------------------------------------------
>
> Key: TEZ-4069
> URL: https://issues.apache.org/jira/browse/TEZ-4069
> Project: Apache Tez
> Issue Type: Improvement
> Affects Versions: 0.9.2
> Reporter: Oliver Draese
> Priority: Major
> Attachments: TEZ-4069.1.patch, TEZ-4069.patch
>
>
> The TezSplitGrouper iterates through the list of splits multiple times, when
> trying to group the splits (see getGroupedSplits). Each time, it asks the
> locationProvider to return the array of preferred locations for the splits.
> This has two side effects:
> * generating the list of preferred locations can cause some CPU overhead
> (i.e. calculating the consistent hash in HostAffinitySplitLocationProvider),
> which can be avoided
> * if the list of preferred location is changing between the different loops
> of getGroupedSplits, we might encounter a NullPointerException. This happens
> if a new location appears, that was not part of the initial set of locations
> when populating the distinctLocations map.
> The getGroupedSplits should query the preferred locations only once (for each
> split) via the location provider and then memorize these instead of asking
> the location provider repeatedly.
>
>
>
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