GitHub user davies opened a pull request:
https://github.com/apache/spark/pull/10228
[SPARK-12213] [SQL] use multiple partitions for single distinct query
Currently, we could generate different plans for query with single distinct
(depends on spark.sql.specializeSingleDistinctAggPlanning), one works better on
low cardinality columns, the other
works better for high cardinality column (default one).
This PR change to generate a single plan (three aggregations and two
exchanges), which work better in both cases, then we could safely remove the
flag `spark.sql.specializeSingleDistinctAggPlanning` (introduced in 1.6).
cc @yhuai @nongli @marmbrus
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/davies/spark single_distinct
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/10228.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #10228
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commit e3f2e79a5e6da3fcfe7d0441dd00cb31f3a30992
Author: Davies Liu <[email protected]>
Date: 2015-12-09T19:05:25Z
use multiple partitions for single distinct query
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