GitHub user davies opened a pull request:
https://github.com/apache/spark/pull/11788
[SPARK-13977] [SQL] Brings back Shuffled hash join
## What changes were proposed in this pull request?
ShuffledHashJoin (also outer join) is removed in 1.6, in favor of
SortMergeJoin, which is more robust and also fast.
ShuffledHashJoin is still useful in this case: 1) one table is much smaller
than the other one, then cost to build a hash table on smaller table is smaller
than sorting the larger table 2) any partition of the small table could fit in
memory.
This PR brings back ShuffledHashJoin, basically revert #9645, and fix the
conflict. Also merging outer join and left-semi join into the same class. This
PR does not implement full outer join, because it's not implemented efficiently
(requiring build hash table on both side).
A simple benchmark (one table is 5x smaller than other one) show that
ShuffledHashJoin could be 2X faster than SortMergeJoin.
## How was this patch tested?
Added new unit tests for ShuffledHashJoin.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/davies/spark shuffle_join
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/11788.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 #11788
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commit c8d2aa0ed599196a62c4c176e2a4c3b337feb171
Author: Davies Liu <dav...@databricks.com>
Date: 2016-03-17T07:26:37Z
shuffle hash join
commit 450c4be6665268798708cce168ca97e243647f2a
Author: Davies Liu <dav...@databricks.com>
Date: 2016-03-17T17:18:30Z
fix indentsin SMJ
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