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https://issues.apache.org/jira/browse/IMPALA-11040?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17451490#comment-17451490
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Sheng Wang commented on IMPALA-11040:
-------------------------------------
Thanks for testing, [~stigahuang]. You are rigiht, this query is too slow. But
with more nested union stmt, the query will take hours times, and even failed.
I will try to locate the performance issue.
> Query get stuck when containing multiple nested union
> -----------------------------------------------------
>
> Key: IMPALA-11040
> URL: https://issues.apache.org/jira/browse/IMPALA-11040
> Project: IMPALA
> Issue Type: Question
> Components: Frontend
> Affects Versions: Impala 4.0.0
> Reporter: Sheng Wang
> Assignee: Sheng Wang
> Priority: Major
>
> When query contains multiple union, and encounter a expr rewrite. Then this
> query will do 'reAnalyze', and get stuck in 'reset' method. Here is the
> example to reproduce this bug:
> {code:java}
> SELECT `t1`.`dt`
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM
>
> (SELECT *
> FROM
>
> (SELECT *
>
> FROM
>
> (SELECT *
>
> FROM
>
> (SELECT *
>
> FROM
>
> (SELECT *
>
> FROM
>
> (SELECT *
>
> FROM
>
> (SELECT *
>
> FROM
>
> (SELECT '20211020' AS `dt`
>
> UNION ALL SELECT '20211021' AS `dt`) AS `t`
>
> UNION ALL SELECT '20211022' AS `dt`) AS `t`
>
> UNION ALL SELECT '20211023' AS `dt`) AS `t`
>
> UNION ALL SELECT '20211024' AS `dt`) AS `t`
>
> UNION ALL SELECT '20211025' AS `dt`) AS `t`
>
> UNION ALL SELECT '20211026' AS `dt`) AS `t`
>
> UNION ALL SELECT '20211027' AS `dt`) AS `t`
> UNION
> ALL SELECT '20211028' AS `dt`) AS `t`
> UNION
> ALL SELECT '20211029' AS `dt`) AS `t`
> UNION ALL
> SELECT '20211030' AS `dt`) AS `t`
> UNION ALL
> SELECT '20211031' AS `dt`) AS `t`
> UNION ALL SELECT
> '20211101' AS `dt`) AS `t`
> UNION ALL SELECT
> '20211102' AS `dt`) AS `t`
> UNION ALL SELECT
> '20211103' AS `dt`) AS `t`
> UNION ALL SELECT
> '20211104' AS `dt`) AS `t`
> UNION ALL SELECT '20211105'
> AS `dt`) AS `t`
> UNION ALL SELECT '20211106' AS
> `dt`) AS `t`
> UNION ALL SELECT '20211107' AS
> `dt`) AS `t`
> UNION ALL SELECT '20211108' AS `dt`)
> AS `t`
> UNION ALL SELECT '20211109' AS `dt`) AS
> `t`
> UNION ALL SELECT '20211110' AS `dt`) AS `t`
> UNION ALL SELECT '20211111' AS `dt`) AS `t`
> UNION ALL SELECT '20211112' AS `dt`) AS `t`
> UNION ALL SELECT '20211113' AS `dt`) AS `t`
> UNION ALL SELECT '20211114' AS `dt`) AS `t`
> UNION ALL SELECT '20211115' AS `dt`) AS `t`
> UNION ALL SELECT '20211116' AS `dt`) AS `t`
> UNION ALL SELECT '20211117' AS `dt`) AS `t`
> UNION ALL SELECT '20211118' AS `dt`) AS `t`
> UNION ALL SELECT '20211119' AS `dt`) AS `t`
> UNION ALL SELECT '20211120' AS `dt`) AS `t1`
> CROSS JOIN
> (SELECT 1000+1000) AS `t2`
> GROUP BY `t1`.`dt`;
> {code}
> This query may take long time to execute, such as ten minutes. If we reduce
> 'UNION', the query will execute quickly.
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