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From "Hive QA (Jira)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-20983) Vectorization: Scale up small hashtables, when collisions are detected
Date Sun, 15 Sep 2019 22:32:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-20983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16930160#comment-16930160
] 

Hive QA commented on HIVE-20983:
--------------------------------



Here are the results of testing the latest attachment:
https://issues.apache.org/jira/secure/attachment/12980354/HIVE-20983.4.patch

{color:green}SUCCESS:{color} +1 due to 7 test(s) being added or modified.

{color:red}ERROR:{color} -1 due to 2 failed/errored test(s), 16727 tests executed
*Failed tests:*
{noformat}
TestDataSourceProviderFactory - did not produce a TEST-*.xml file (likely timed out) (batchId=233)
TestObjectStore - did not produce a TEST-*.xml file (likely timed out) (batchId=233)
{noformat}

Test results: https://builds.apache.org/job/PreCommit-HIVE-Build/18606/testReport
Console output: https://builds.apache.org/job/PreCommit-HIVE-Build/18606/console
Test logs: http://104.198.109.242/logs/PreCommit-HIVE-Build-18606/

Messages:
{noformat}
Executing org.apache.hive.ptest.execution.TestCheckPhase
Executing org.apache.hive.ptest.execution.PrepPhase
Executing org.apache.hive.ptest.execution.YetusPhase
Executing org.apache.hive.ptest.execution.ExecutionPhase
Executing org.apache.hive.ptest.execution.ReportingPhase
Tests exited with: TestsFailedException: 2 tests failed
{noformat}

This message is automatically generated.

ATTACHMENT ID: 12980354 - PreCommit-HIVE-Build

> Vectorization: Scale up small hashtables, when collisions are detected
> ----------------------------------------------------------------------
>
>                 Key: HIVE-20983
>                 URL: https://issues.apache.org/jira/browse/HIVE-20983
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Gopal V
>            Assignee: Mustafa Iman
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: HIVE-20983.1.patch, HIVE-20983.2.patch, HIVE-20983.3.patch, HIVE-20983.4.patch
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> Hive's hashtable estimates are getting better with HyperLogLog stats in place, but an
accurate estimate does not always result in a low number of collisions.
> The hashtables which contain a very small number of items tend to lose their O(1) lookup
performance where there are collisions. Since collisions are easy to detect within the fast
hashtable implementation, a rehashing to a higher size will help these small hashtables avoid
collisions and go back to O(1) perf.



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