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Posted to issues@spark.apache.org by "Josh Rosen (JIRA)" <ji...@apache.org> on 2019/06/06 23:06:00 UTC
[jira] [Commented] (SPARK-27761) Make UDF nondeterministic by
default(?)
[ https://issues.apache.org/jira/browse/SPARK-27761?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16858155#comment-16858155 ]
Josh Rosen commented on SPARK-27761:
------------------------------------
FYI, I'm marking SPARK-27969 as a blocker to this because non-deterministic expressions can unnecessarily prevent scan-time column pruning: as a result, a change of default could lead to massive performance regressions when users upgrade to 3.0.
> Make UDF nondeterministic by default(?)
> ---------------------------------------
>
> Key: SPARK-27761
> URL: https://issues.apache.org/jira/browse/SPARK-27761
> Project: Spark
> Issue Type: Brainstorming
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Sunitha Kambhampati
> Priority: Minor
>
> Opening this issue as a followup from a discussion/question on this PR for an optimization involving deterministic udf: https://github.com/apache/spark/pull/24593#pullrequestreview-237361795
> "We even should discuss whether all UDFs must be deterministic or non-deterministic by default."
> Basically today in Spark 2.4, Scala UDFs are marked deterministic by default and it is implicit. To mark a udf as non deterministic, they need to call this method asNondeterministic().
> The concern's expressed are that users are not aware of this property and its implications.
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