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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4530) Improve metadata cache performance for queries with single partition
Date Wed, 13 Jul 2016 00:52:20 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15374090#comment-15374090
] 

ASF GitHub Bot commented on DRILL-4530:
---------------------------------------

Github user amansinha100 commented on a diff in the pull request:

    https://github.com/apache/drill/pull/519#discussion_r70548891
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/ParquetGroupScan.java
---
    @@ -607,7 +607,14 @@ public long getRowCount() {
           fileSet = Sets.newHashSet(fileNames);
         }
     
    -    if (fileNames.isEmpty()) {
    +    List<String> finalFileNames;
    +    if (fileSet != null) {
    +      finalFileNames = Lists.newArrayList(fileSet);
    --- End diff --
    
    Yes, I can try to keep only the fileSet and get rid of fileNames (although I would still
need the finalFileNames list since FileSelection only accepts a List, not a Set).


> 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: Future
>
>
> 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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