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https://issues.apache.org/jira/browse/DRILL-4530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15326690#comment-15326690
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Aman Sinha commented on DRILL-4530:
-----------------------------------
I have created a PR for this. All unit and functional tests are clean. I
haven't yet run performance tests. The changes are in 3 broad areas: (a)
file/dir selection (b) partition pruning, (c) metadata cache. The changes in
(a) and (b) are mostly independent of the changes in (c) which relies on a
separate directories file. In the future we could swap out the changes in (c)
whenever the metadata cache is enhanced to allow faster access to the
directories field.
Feedback is welcome.
> Improve metadata cache performance for queries with single partition
> ---------------------------------------------------------------------
>
> Key: DRILL-4530
> URL: https://issues.apache.org/jira/browse/DRILL-4530
> Project: Apache Drill
> Issue Type: Improvement
> Components: Query Planning & Optimization
> Affects Versions: 1.6.0
> Reporter: Aman Sinha
> Assignee: Aman Sinha
> Fix For: 1.7.0
>
>
> Consider two types of queries which are run with Parquet metadata caching:
> {noformat}
> query 1:
> SELECT col FROM `A/B/C`;
> query 2:
> SELECT col FROM `A` WHERE dir0 = 'B' AND dir1 = 'C';
> {noformat}
> For a certain dataset, the query1 elapsed time is 1 sec whereas query2
> elapsed time is 9 sec even though both are accessing the same amount of data.
> The user expectation is that they should perform roughly the same. The main
> difference comes from reading the bigger metadata cache file at the root
> level 'A' for query2 and then applying the partitioning filter. query1 reads
> a much smaller metadata cache file at the subdirectory level.
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