[SPARK-19426][SQL] Custom coalescer for Dataset #46541
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SubhamSinghal
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Can you walk me through the actual use case for this? Coalesce - historically - is incredibly hard to use for most end user, so before adding this I'd like to understand why. |
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Coalesce does not enforce uniform data distribution across partitions. We would like to pass custom size based coalescer to have more uniform data distribution. This would avoid using repartition and shuffle at places. |
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@hvanhovell will you be able to add review here or tag relevant folks? |
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What changes were proposed in this pull request?
This pr adds a new API for coalesce in Dataset; users can specify the custom coalescer which reduces an input Dataset into fewer partitions. This coalescer implementation is the same with the one in RDD#coalesce added in #11865 (SPARK-14042).
This is the rework of #18861.
How was this patch tested?
Added tests in DatasetSuite.