You are viewing a plain text version of this content. The canonical link for it is here.

Posted to issues-all@impala.apache.org by "Riza Suminto (Jira)" <ji...@apache.org> on 2023/06/22 05:50:00 UTC

[jira] [Resolved] (IMPALA-12200) Cap stats NDV from SetOperationStmt.createMetadata

     [ https://issues.apache.org/jira/browse/IMPALA-12200?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Riza Suminto resolved IMPALA-12200.
-----------------------------------
    Fix Version/s: Impala 4.3.0
       Resolution: Fixed

> Cap stats NDV from SetOperationStmt.createMetadata
> --------------------------------------------------
>
>                 Key: IMPALA-12200
>                 URL: https://issues.apache.org/jira/browse/IMPALA-12200
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Frontend
>    Affects Versions: Impala 4.3.0
>            Reporter: Riza Suminto
>            Assignee: Riza Suminto
>            Priority: Major
>             Fix For: Impala 4.3.0
>
>
> Union operator will create merged ColumnStats at SetOperationStmt.createMetadata where it adds all ColumnStats from its input children. One of the stats being accumulated is NDV (num distinct value). There is an opportunity to lower the resulting NDV if all source expression is referring to the same column. This lower NDV can benefit Aggregation node on top of the Union node because it can lower cardinality and memory estimate of the Aggregation node.



--
This message was sent by Atlassian Jira
(v8.20.10#820010)

---------------------------------------------------------------------
To unsubscribe, e-mail: issues-all-unsubscribe@impala.apache.org
For additional commands, e-mail: issues-all-help@impala.apache.org