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https://issues.apache.org/jira/browse/SPARK-32755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17187779#comment-17187779
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Apache Spark commented on SPARK-32755:
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User 'dbaliafroozeh' has created a pull request for this issue:
https://github.com/apache/spark/pull/29598
> Maintain the order of expressions in AttributeSet and ExpressionSet
> --------------------------------------------------------------------
>
> Key: SPARK-32755
> URL: https://issues.apache.org/jira/browse/SPARK-32755
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.1.0
> Reporter: Ali Afroozeh
> Priority: Major
>
> Expressions identity is based on the ExprId which is an auto-incremented
> number. This means that the same query can yield a query plan with different
> expression ids in different runs. AttributeSet and ExpressionSet internally
> use a HashSet as the underlying data structure, and therefore cannot
> guarantee the a fixed order of operations in different runs. This can be
> problematic in cases we like to check for plan changes in different runs.
> We change do the following changes to AttributeSet and ExpressionSet to
> maintain the insertion order of the elements:
> * We change the underlying data structure of AttributeSet from HashSet to
> LinkedHashSet to maintain the insertion order.
> * ExpressionSet already uses a list to keep track of the expressions,
> however, since it is extending Scala's immutable.Set class, operations such
> as map and flatMap are delegated to the immutable.Set itself. This means that
> the result of these operations is not an instance of ExpressionSet anymore,
> rather it's a implementation picked up by the parent class. We also remove
> this inheritance from immutable.Set and implement the needed methods
> directly. ExpressionSet has a very specific semantics and it does not make
> sense to extend immutable.Set anyway.
> * We change the PlanStabilitySuite to not sort the attributes, to be able to
> catch changes in the order of expressions in different runs.
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