GitHub user gatorsmile opened a pull request:
https://github.com/apache/spark/pull/10630
[SPARK-12656] [SQL] Implement Intersect with Left-semi Join
Our current Intersect physical operator simply delegates to RDD.intersect.
We should remove the Intersect physical operator and simply transform a logical
intersect into a semi-join. This way, we can take advantage of all the benefits
of join implementations (e.g. managed memory, code generation, broadcast joins).
After a search, I found one of the mainstream RDBMS did the same. In their
query explain, Intersect is replaced by Left-semi Join. Left-semi Join could
help outer-join elimination in Optimizer, as shown in the PR:
https://github.com/apache/spark/pull/10566
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/gatorsmile/spark IntersectBySemiJoin
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/10630.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 #10630
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commit 0bd177135bc1c8210fa0ea5a8c7a4c5144d6227e
Author: gatorsmile <[email protected]>
Date: 2016-01-07T05:40:33Z
replace Intersect with Left-semi Join
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