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Posted to issues@hive.apache.org by "ASF GitHub Bot (Jira)" <ji...@apache.org> on 2019/10/15 03:04:00 UTC
[jira] [Work logged] (HIVE-20983) Vectorization: Scale up small
hashtables, when collisions are detected
[ https://issues.apache.org/jira/browse/HIVE-20983?focusedWorklogId=328278&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-328278 ]
ASF GitHub Bot logged work on HIVE-20983:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 15/Oct/19 03:03
Start Date: 15/Oct/19 03:03
Worklog Time Spent: 10m
Work Description: jcamachor commented on pull request #771: HIVE-20983
URL: https://github.com/apache/hive/pull/771
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Issue Time Tracking
-------------------
Worklog Id: (was: 328278)
Time Spent: 20m (was: 10m)
> 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 Vijayaraghavan
> Assignee: Mustafa Iman
> Priority: Major
> Labels: pull-request-available
> Fix For: 4.0.0
>
> Attachments: HIVE-20983.1.patch, HIVE-20983.2.patch, HIVE-20983.3.patch, HIVE-20983.4.patch, HIVE-20983.5.patch
>
> Time Spent: 20m
> 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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