GitHub user wzhfy opened a pull request:
https://github.com/apache/spark/pull/17240
[SPARK-17080][SQL][followup] simplify algorithm
## What changes were proposed in this pull request?
1. Do column pruning during reordering is troublesome. We can do it right
after reordering, then logics for adding projects on intermediate joins can be
removed. This makes the code simpler and more reliable.
2. Usually cardinality is more important than size, we can simplify cost
evaluation by using only cardinality. Note that this enables us to not care
about column pruing during reordering (the first point). Otherwise, project
will influence the output size of intermediate joins.
3. Exclude cartesian products in the "memo". This significantly reduce the
search space. 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.
## How was this patch tested?
Not related.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/wzhfy/spark joinReorder2
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/17240.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 #17240
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commit 94bc9355b647f181549c8a11d77b00237ea4c528
Author: wangzhenhua <[email protected]>
Date: 2017-03-10T08:33:46Z
1.don't deal with projects during reordering 2.exclude cartesian products
during reordering 3.only use cardinality as cost.
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