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https://issues.apache.org/jira/browse/DRILL-7490?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17164480#comment-17164480
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mustafa Erkoç commented on DRILL-7490:
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this issue has a two problems
1. does not push down all limit values except limit 10 (only limit 10
pushdown)
2. pushdown only when a single column is selected. does not pushdown when
multiple columns are selected
The following query:
!image-2020-07-24-17-45-27-357.png!
!image-2020-07-24-17-46-05-219.png!
!image-2020-07-24-17-46-59-584.png!
!image-2020-07-24-17-48-53-740.png!
N
> limit is not pushed to JDBC storage plugin
> ------------------------------------------
>
> Key: DRILL-7490
> URL: https://issues.apache.org/jira/browse/DRILL-7490
> Project: Apache Drill
> Issue Type: Bug
> Components: Query Planning & Optimization, Storage - JDBC
> Affects Versions: 1.11.0
> Reporter: Vova Vysotskyi
> Assignee: Vova Vysotskyi
> Priority: Major
> Labels: ready-to-commit
> Fix For: 1.17.0
>
> Attachments: image-2020-07-24-17-31-02-589.png,
> image-2020-07-24-17-31-48-831.png, image-2020-07-24-17-35-28-912.png,
> image-2020-07-24-17-45-27-357.png, image-2020-07-24-17-46-05-219.png,
> image-2020-07-24-17-46-59-584.png, image-2020-07-24-17-48-53-740.png
>
>
> The limit is not pushed to JDBC storage plugin.
> The following query:
> {code:sql}
> select person_id from mysql.`drill_mysql_test`.person limit 10
> {code}
> Returns plan:
> {noformat}
> 00-00 Screen
> 00-01 Project(person_id=[$0])
> 00-02 SelectionVectorRemover
> 00-03 Limit(fetch=[10])
> 00-04 Limit(fetch=[10])
> 00-05 Jdbc(sql=[SELECT `person_id` FROM
> `drill_mysql_test`.`person` ])
> {noformat}
> This issue happens since incorrect row count is calculated for {{JdbcSort}}.
> Drill enforces to use {{RelNode.estimateRowCount(mq)}} for calculating row
> count for all inheritants of {{Sort}} rel node (see {{DrillRelMdRowCount}}),
> but {{JdbcSort}} doesn't override this method and uses parent one which
> returns row count of input. So planner choses {{DrillLimitRel}} since it has
> less row count.
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