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https://issues.apache.org/jira/browse/DRILL-8290?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17679170#comment-17679170
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ASF GitHub Bot commented on DRILL-8290:
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jnturton commented on PR #2636:
URL: https://github.com/apache/drill/pull/2636#issuecomment-1398472306
> For such queries the same QueryComputationHints will be used for both
inputs, so it will cause incorrect results.
@vvysotskyi the idea here was that only a LIMIT 0 on the _root_ SELECT is
detected, in which case the single file optimisation can be done on _all_
inputs so a single flag is sufficient.
However, I'm trying to implement a better approach that optimises LIMIT 0s
at any level. Since files are first listed very early, during validation (so
even before partition pruning 🙁) no RelNode trees are available and the
detection will have to be done on the SqlNode tree.
> Short cut recursive file listings for LIMIT 0 queries
> -----------------------------------------------------
>
> Key: DRILL-8290
> URL: https://issues.apache.org/jira/browse/DRILL-8290
> Project: Apache Drill
> Issue Type: Improvement
> Components: Query Planning & Optimization
> Affects Versions: 1.20.2
> Reporter: James Turton
> Priority: Minor
> Fix For: 1.21.0
>
>
> The existing LIMIT 0 query optimisations do not prevent a query run against
> the top of a deep DFS directory tree from recursively listing FileStatuses
> for everything within it using a pool of worker threads. This Issue proposes
> a new optimisation whereby such queries will recurse into the directory tree
> on a single thread that returns as soon as any single FileStatus has been
> obtained.
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