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https://issues.apache.org/jira/browse/DRILL-3952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14976946#comment-14976946
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Deneche A. Hakim commented on DRILL-3952:
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[~amansinha100] can you please review ? thx
> Improve Window Functions performance when not all batches are required to
> process the current batch
> ---------------------------------------------------------------------------------------------------
>
> Key: DRILL-3952
> URL: https://issues.apache.org/jira/browse/DRILL-3952
> Project: Apache Drill
> Issue Type: Bug
> Components: Execution - Relational Operators
> Affects Versions: 1.2.0
> Reporter: Deneche A. Hakim
> Assignee: Aman Sinha
> Fix For: 1.3.0
>
>
> Currently, the window operator blocks until all batches of current partition
> to be available. For some queries it's necessary (e.g. aggregate with no
> order-by in the window definition), but for other cases the window operator
> can process and pass the current batch downstream sooner.
> Implementing this should help the window operator use less memory and run
> faster, especially in the presence of a limit operator.
> The purpose of this JIRA is to improve the window operator in the following
> cases:
> - aggregate, when order-by clause is available in window definition, can
> process current batch as soon as it receives the last peer row
> - lead can process current batch as soon as it receives 1 more batch
> - lag can process current batch immediately
> - first_value can process current batch immediately
> - last_value, when order-by clause is available in window definition, can
> process current batch as soon as it receives the last peer row
> - row_number, rank and dense_rank can process current batch immediately
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