GitHub user wzhfy opened a pull request:
https://github.com/apache/spark/pull/17286
[SPARK-19915][SQL] Exclude cartesian product results in join reorder
## What changes were proposed in this pull request?
Exclude cartesian products in the "memo". This significantly reduces the
search space and memory overhead of memo. Otherwise every combination of items
will exist in the memo. We can find those unjoinable items after reordering is
finished and put them at the end.
This pr also includes a bug fix: if a leaf item is a project(_, child),
current solution will miss the project.
## How was this patch tested?
Add a test case.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/wzhfy/spark joinReorder3
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/17286.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 #17286
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commit f472c74189f5f54c701876aaa73f7d331e5b814d
Author: wangzhenhua <[email protected]>
Date: 2017-03-14T08:15:45Z
improve join reorder
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