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Posted to issues@spark.apache.org by "Apache Spark (Jira)" <ji...@apache.org> on 2020/09/25 16:57:00 UTC
[jira] [Assigned] (SPARK-32995) CostBasedJoinReorder optimizer rule
should be idempotent
[ https://issues.apache.org/jira/browse/SPARK-32995?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Apache Spark reassigned SPARK-32995:
------------------------------------
Assignee: (was: Apache Spark)
> CostBasedJoinReorder optimizer rule should be idempotent
> --------------------------------------------------------
>
> Key: SPARK-32995
> URL: https://issues.apache.org/jira/browse/SPARK-32995
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.1.0
> Reporter: Tanel Kiis
> Priority: Minor
>
> The CostBasedJoinReorder has currently the following comment:
> {code}
> // Since join costs in AQP can change between multiple runs, there is no reason that we have an
> // idempotence enforcement on this batch. We thus make it FixedPoint(1) instead of Once.
> {code}
> This is incorrect reasoning.
> In the optimizer, we mean that a batch is idempotent, when applying it for the second time in a row (without changing anything) it does not change the plan at all.
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