[ 
https://issues.apache.org/jira/browse/HIVE-15796?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Chao Sun updated HIVE-15796:
----------------------------
    Attachment: HIVE-15796.2.patch

> HoS: poor reducer parallelism when operator stats are not accurate
> ------------------------------------------------------------------
>
>                 Key: HIVE-15796
>                 URL: https://issues.apache.org/jira/browse/HIVE-15796
>             Project: Hive
>          Issue Type: Improvement
>          Components: Statistics
>    Affects Versions: 2.2.0
>            Reporter: Chao Sun
>            Assignee: Chao Sun
>         Attachments: HIVE-15796.1.patch, HIVE-15796.2.patch, 
> HIVE-15796.wip.1.patch, HIVE-15796.wip.2.patch, HIVE-15796.wip.patch
>
>
> In HoS we use currently use operator stats to determine reducer parallelism. 
> However, it is often the case that operator stats are not accurate, 
> especially if column stats are not available. This sometimes will generate 
> extremely poor reducer parallelism, and cause HoS query to run forever. 
> This JIRA tries to offer an alternative way to compute reducer parallelism, 
> similar to how MR does. Here's the approach we are suggesting:
> 1. when computing the parallelism for a MapWork, use stats associated with 
> the TableScan operator;
> 2. when computing the parallelism for a ReduceWork, use the *maximum* 
> parallelism from all its parents.



--
This message was sent by Atlassian JIRA
(v6.3.15#6346)

Reply via email to