GitHub user gengliangwang opened a pull request:
https://github.com/apache/spark/pull/19064
[SPARK-21848][SQL] Add trait UDFType to identify user-defined functions
## What changes were proposed in this pull request?
Add trait UDFType to identify user-defined functions.
UDF can be expensive. In optimizer we may need to avoid executing UDF
multiple times.
E.g.
```scala
table.select(UDF as 'a).select('a, '(a + 1))
```
If UDF is expensive in this case, optimizer should not collapse the project
to
```scala
table.select(UDF as 'a, (UDF+1) as '(a+1))
```
Currently UDF classes like PythonUDF, HiveGenericUDF are not defined in
catalyst.
This PR is to add a new trait to make it easier to identify user-defined
functions.
## How was this patch tested?
Unit test
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/gengliangwang/spark UDFType
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/19064.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 #19064
----
commit 5f508ab0b1bf91f7a857adabbefea399c8a71005
Author: Wang Gengliang <ltn...@gmail.com>
Date: 2017-08-26T13:15:15Z
add trait UDFType to identify UDF classes
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