Oliver Draese created TEZ-4069:
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Summary: 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
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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