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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 Sat, 16 Jul 2016 02:29:20 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15380437#comment-15380437
] 

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_r71059510
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/partition/PruneScanRule.java
---
    @@ -143,6 +144,11 @@ public static final RelOptRule getDirFilterOnScan(OptimizerRulesContext
optimize
       }
     
       protected void doOnMatch(RelOptRuleCall call, Filter filterRel, Project projectRel,
TableScan scanRel) {
    +    if (wasAllPartitionsPruned) {
    --- End diff --
    
    Pls see commit #ce509af for the changes.  Since the 'all partitions pruned' is a special
case, I had to keep track of this state and propagate it during the new FileSelection creation
after partition pruning. Thus, if the first phase directory pruning eliminated all partitions
and we re-added 1 for schema purposes, this directory selection will be  eventually seen by
the ParquetGroupScan which will examine a flag 'wasAllPartitionsPruned' and decide to retrieve
only 1 file from this directory.  


> 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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