[jira] [Commented] (DRILL-4530) Improve metadata cache performance for queries with single partition

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-4530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15366914#comment-15366914 ] 

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_r70002215
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/partition/PruneScanRule.java ---
    @@ -269,13 +283,54 @@ protected void doOnMatch(RelOptRuleCall call, Filter filterRel, Project projectR
             int recordCount = 0;
             int qualifiedCount = 0;
     
    -        // Inner loop: within each batch iterate over the PartitionLocations
    -        for(PartitionLocation part: partitions){
    -          if(!output.getAccessor().isNull(recordCount) && output.getAccessor().get(recordCount) == 1){
    -            newPartitions.add(part);
    -            qualifiedCount++;
    +        if (checkForSingle &&
    +            partitions.get(0).isCompositePartition() /* apply single partition check only for composite partitions */) {
    +          // Inner loop: within each batch iterate over the PartitionLocations
    +          for (PartitionLocation part : partitions) {
    +            assert part.isCompositePartition();
    +            if(!output.getAccessor().isNull(recordCount) && output.getAccessor().get(recordCount) == 1) {
    +              newPartitions.add(part);
    +              if (isSinglePartition) { // only need to do this if we are already single partition
    +                // compose the array of partition values for the directories that are referenced by filter:
    +                // e.g suppose the dir hierarchy is year/quarter/month and the query is:
    +                //     SELECT * FROM T WHERE dir0=2015 AND dir1 = 'Q1',
    +                // then for 2015/Q1/Feb, this will have ['2015', 'Q1', null]
    --- End diff --
    
    I have fixed this case and updated the pull request with a separate commit (not squashed yet so you can review it separately). 


> 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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