GitHub user viirya opened a pull request:
https://github.com/apache/spark/pull/14327
[SPARK-16686][SQL] Project shouldn't be pushed down through Sample if it
has new output
## What changes were proposed in this pull request?
We push down `Project` through `Sample` in `Optimizer`. However, if the
projected columns produce new output, they will encounter whole data instead of
sampled data. It will bring some inconsistency between original plan (Sample
then Project) and optimized plan (Project then Sample). In the extreme case
such as attached in the JIRA, if the projected column is an UDF which is
supposed to not see the sampled out data, the result of UDF will be incorrect.
We shouldn't push down Project through Sample if the Project brings new
output.
## How was this patch tested?
Jenkins tests.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/viirya/spark-1 fix-sample-pushdown
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/14327.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 #14327
----
commit 9521a5aca87bead3dcfeabd7abe3468194984ea3
Author: Liang-Chi Hsieh <sim...@tw.ibm.com>
Date: 2016-07-23T10:13:07Z
Project shouldn't be pushed down through Sample if it has new output.
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