Tanel Kiis created SPARK-32995:
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Summary: 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
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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