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From "Robert Hou (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-5774) Excessive memory allocation
Date Thu, 07 Sep 2017 22:05:00 GMT
Robert Hou created DRILL-5774:
---------------------------------

             Summary: Excessive memory allocation
                 Key: DRILL-5774
                 URL: https://issues.apache.org/jira/browse/DRILL-5774
             Project: Apache Drill
          Issue Type: Bug
          Components: Execution - Relational Operators
    Affects Versions: 1.11.0
            Reporter: Robert Hou
            Assignee: Paul Rogers
             Fix For: 1.12.0


This query exhibits excessive memory allocation:
{noformat}
ALTER SESSION SET `exec.sort.disable_managed` = false;
alter session set `planner.width.max_per_node` = 1;
alter session set `planner.disable_exchanges` = true;
alter session set `planner.width.max_per_query` = 1;
select count(*) from (select * from (select id, flatten(str_list) str from dfs.`/drill/testdata/resource-manager/flatten-large-small.json`)
d order by d.str) d1 where d1.id=0;
{noformat}

This query does a flatten on a large table.  The result is 160M records.  Half the records
have a one-byte string, and half have a 253-byte string.  And then there are 40K records with
223 byte strings.

{noformat}
select length(str), count(*) from (select id, flatten(str_list) str from dfs.`/drill/testdata/resource-manager/flatten-large-small.json`)
group by length(str);
+---------+-----------+
| EXPR$0  |  EXPR$1   |
+---------+-----------+
| 223     | 40000     |
| 1       | 80042001  |
| 253     | 80000000  |
{noformat}

>From the drillbit.log:
{noformat}
2017-09-02 11:43:44,598 [26550427-6adf-a52e-2ea8-dc52d8d8433f:frag:0:0] DEBUG o.a.d.e.p.i.x.m.ExternalSortBatch
- Actual batch schema & sizes {
  str(type: REQUIRED VARCHAR, count: 4096, std size: 54, actual size: 134, data size: 548360)
  id(type: OPTIONAL BIGINT, count: 4096, std size: 8, actual size: 9, data size: 36864)
  Records: 4096, Total size: 1073819648, Data size: 585224, Gross row width: 262163, Net row
width: 143, Density: 1}
{noformat}

The data size is 585K, but the batch size is 1 GB.  The density is 1%.



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