Min Shen created SPARK-30602:
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Summary: Support push-based shuffle to improve shuffle efficiency
Key: SPARK-30602
URL: https://issues.apache.org/jira/browse/SPARK-30602
Project: Spark
Issue Type: Improvement
Components: Shuffle
Affects Versions: 3.0.0
Reporter: Min Shen
In a large deployment of a Spark compute infrastructure, Spark shuffle is
becoming a potential scaling bottleneck and a source of inefficiency in the
cluster. When doing Spark on YARN for a large-scale deployment, people usually
enable Spark external shuffle service and store the intermediate shuffle files
on HDD. Because the number of blocks generated for a particular shuffle grows
quadratically compared to the size of shuffled data (# mappers and reducers
grows linearly with the size of shuffled data, but # blocks is # mappers * #
reducers), one general trend we have observed is that the more data a Spark
application processes, the smaller the block size becomes. In a few production
clusters we have seen, the average shuffle block size is only 10s of KBs.
Because of the inefficiency of performing random reads on HDD for small amount
of data, the overall efficiency of the Spark external shuffle services serving
the shuffle blocks degrades as we see an increasing # of Spark applications
processing an increasing amount of data. In addition, because Spark external
shuffle service is a shared service in a multi-tenancy cluster, the
inefficiency with one Spark application could propagate to other applications
as well.
In this ticket, we propose a solution to improve Spark shuffle efficiency in
above mentioned environments with push-based shuffle. With push-based shuffle,
shuffle is performed at the end of mappers and blocks get pre-merged and move
towards reducers. In our prototype implementation, we have seen significant
efficiency improvements when performing large shuffles. We take a Spark-native
approach to achieve this, i.e., extending Spark’s existing shuffle netty
protocol, and the behaviors of Spark mappers, reducers and drivers. This way,
we can bring the benefits of more efficient shuffle in Spark without incurring
the dependency or overhead of either specialized storage layer or external
infrastructure pieces.
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