[jira] [Commented] (DRILL-5502) Parallelized external sort is slower compared to the single fragment scenario on some data sets

["Rahul Challapalli (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-5502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16007386#comment-16007386 ] 

Rahul Challapalli commented on DRILL-5502:
------------------------------------------

I couldn't reproduce this when the column size is < 256 bytes. So it has something to do with wide columns

> Parallelized external sort is slower compared to the single fragment scenario on some data sets
> -----------------------------------------------------------------------------------------------
>
>                 Key: DRILL-5502
>                 URL: https://issues.apache.org/jira/browse/DRILL-5502
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Execution - Relational Operators
>    Affects Versions: 1.10.0
>            Reporter: Rahul Challapalli
>            Assignee: Paul Rogers
>         Attachments: multiple_fragments.log, multiple_fragments.sys.drill, single_fragment.log, single_fragment.sys.drill
>
>
> git.commit.id.abbrev=1e0a14c
> The below query runs in a single fragment and completes in ~13 minutes
> {code}
> ALTER SESSION SET `exec.sort.disable_managed` = false;
> alter session set `planner.width.max_per_node` = 1;
> alter session set `planner.memory.max_query_memory_per_node` = 62600000;
> alter session set `planner.width.max_per_query` = 17;
> select count(*) from (select * from dfs.`/drill/testdata/resource-manager/5kwidecolumns_500k.tbl` order by columns[0]) d where d.columns[0] = '4041054511';
> +---------+
> | EXPR$0  |
> +---------+
> | 0       |
> +---------+
> 1 row selected (832.705 seconds)
> {code}
> Now I increased the parallelization to 10 and also increased the memory allocated to the sort by 10 times, so that each individual fragments still ends up getting the similar amount of memory. In this case however the query takes ~30 minutes to complete which is strange
> {code}
> ALTER SESSION SET `exec.sort.disable_managed` = false;
> alter session set `planner.width.max_per_node` = 10;
> alter session set `planner.memory.max_query_memory_per_node` = 626000000;
> alter session set `planner.width.max_per_query` = 17;
> select count(*) from (select * from dfs.`/drill/testdata/resource-manager/5kwidecolumns_500k.tbl` order by columns[0]) d where d.columns[0] = '4041054511';
> +---------+
> | EXPR$0  |
> +---------+
> | 0       |
> +---------+
> 1 row selected (1845.508 seconds)
> {code}
> My data set contains wide columns (5k chars wide). I will try to reproduce this with a data set where the column width is < 256 bytes. 
> Attached the data profile and log file from both the scenarios. The data set is too large to attach to a jira



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