Xingbo Jiang created SPARK-43043:
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Summary: Improve the performance of
MapOutputTracker.updateMapOutput
Key: SPARK-43043
URL: https://issues.apache.org/jira/browse/SPARK-43043
Project: Spark
Issue Type: Improvement
Components: Spark Core
Affects Versions: 3.3.2
Reporter: Xingbo Jiang
Inside of MapOutputTracker, there is a line of code which does a linear find
through a mapStatuses collection:
https://github.com/apache/spark/blob/cb48c0e48eeff2b7b51176d0241491300e5aad6f/core/src/main/scala/org/apache/spark/MapOutputTracker.scala#L167
(plus a similar search a few lines down at
https://github.com/apache/spark/blob/cb48c0e48eeff2b7b51176d0241491300e5aad6f/core/src/main/scala/org/apache/spark/MapOutputTracker.scala#L174)
This scan is necessary because we only know the mapId of the updated status and
not its mapPartitionId.
We perform this scan once per migrated block, so if a large proportion of all
blocks in the map are migrated then we get O(n^2) total runtime across all of
the calls.
I think we might be able to fix this by extending ShuffleStatus to have an
OpenHashMap mapping from mapId to mapPartitionId.
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