[
https://issues.apache.org/jira/browse/SPARK-20939?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Lovasoa updated SPARK-20939:
----------------------------
Description:
Currently, while optimizing a query plan, spark pushes filters down the query
plan tree, so that
{code:title=LogicalPlan}
Filter UDF(a)
+- Join Inner, (a = b)
+- Relation
+- Relation
{code}
becomes
{code:title=Optimized LogicalPlan}
Join Inner, (a = b)
+- Filter UDF(a)
+- Relation
+- Filter UDF(b)
+- Relation
{code}
In general, it is a good thing to push down filters as it reduces the number of
records that will go through the join.
However, in the case where the filter is an user-defined function (UDF), we
cannot know if the cost of executing the function twice will be higher than the
eventual cost of joining more elements or not.
So I think that the optimizer shouldn't move the user-defined function in the
query plan tree. The user will still be able to duplicate the function if he
wants to.
See this question on stackoverflow:
https://stackoverflow.com/questions/44291078/how-to-tune-the-query-planner-and-turn-off-an-optimization-in-spark
was:
Currently, while optimizing a query plan, spark pushes filters down the query
plan tree, so that
{{
Filter UDF(a)
+- Join Inner, (a = b)
+- Relation
+- Relation
}}
becomes
{{
Join Inner, (a = b)
+- Filter UDF(a)
+- Relation
+- Filter UDF(b)
+- Relation
}}
In general, it is a good thing to push down filters as it reduces the number of
records that will go through the join.
However, in the case where the filter is an user-defined function (UDF), we
cannot know if the cost of executing the function twice will be higher than the
eventual cost of joining more elements or not.
So I think that the optimizer shouldn't move the user-defined function in the
query plan tree. The user will still be able to duplicate the function if he
wants to.
See this question on stackoverflow:
https://stackoverflow.com/questions/44291078/how-to-tune-the-query-planner-and-turn-off-an-optimization-in-spark
> Do not duplicate user-defined functions while optimizing logical query plans
> ----------------------------------------------------------------------------
>
> Key: SPARK-20939
> URL: https://issues.apache.org/jira/browse/SPARK-20939
> Project: Spark
> Issue Type: Bug
> Components: Optimizer, SQL
> Affects Versions: 2.1.0
> Reporter: Lovasoa
> Priority: Minor
> Labels: logical_plan, optimizer
>
> Currently, while optimizing a query plan, spark pushes filters down the query
> plan tree, so that
> {code:title=LogicalPlan}
> Filter UDF(a)
> +- Join Inner, (a = b)
> +- Relation
> +- Relation
> {code}
> becomes
> {code:title=Optimized LogicalPlan}
> Join Inner, (a = b)
> +- Filter UDF(a)
> +- Relation
> +- Filter UDF(b)
> +- Relation
> {code}
> In general, it is a good thing to push down filters as it reduces the number
> of records that will go through the join.
> However, in the case where the filter is an user-defined function (UDF), we
> cannot know if the cost of executing the function twice will be higher than
> the eventual cost of joining more elements or not.
> So I think that the optimizer shouldn't move the user-defined function in the
> query plan tree. The user will still be able to duplicate the function if he
> wants to.
> See this question on stackoverflow:
> https://stackoverflow.com/questions/44291078/how-to-tune-the-query-planner-and-turn-off-an-optimization-in-spark
--
This message was sent by Atlassian JIRA
(v6.3.15#6346)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
