sunchao opened a new pull request, #82:
URL: https://github.com/apache/arrow-datafusion-comet/pull/82
## Which issue does this PR close?
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Closes #.
## Rationale for this change
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Currently in columnar shuffle, when spills are triggered, Comet will write
sorted shuffle data to disk on the native side. As part of the process, it will
also do row to columnar conversion, and write out the shuffle data in Arrow
format. However, the row to columnar conversion will try to buffer all the
shuffle data in memory before writing them to disk. This will potentially cause
OOM since spills usually are triggered when memory is under pressure, and the
Spark executor may not have enough memory left.
Instead, this PR changes the logic so it no longer buffers all shuffle data
in memory. Instead, it immediately flushes out the data to disk once a certain
threshold has been reached. A (internal) config parameter
`spark.comet.columnar.shuffle.batch.size` is introduced to control the
threshold, and by default it is 8K.
## What changes are included in this PR?
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Changed the logic of writing sorted shuffle data to no longer buffer all
data in memory, but instead batch by batch.
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