[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3325) Pagination with Oracle ROWNUM is sub-optimal

[Richard Birkby (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=37892#action_37892 ] 

Richard Birkby commented on HHH-3325:
-------------------------------------

Hibernate doesn't need the ROWNUM column returned. So why not get rid of it?

SELECT this_.ID AS id3_0_, this_.VERSION AS version3_0_,
this_.NAME AS name3_0_, this_.TYPE AS type3_0_,
this_.marketstatus AS marketst5_3_0_ FROM customer this_ WHERE ROWID in (
SELECT rowid_
FROM (SELECT ROWNUM rownum_, ROWID rowid_ FROM customer
WHERE ROWNUM <= ?)
WHERE rownum_ > ?)
ORDER BY this_.ID ASC

Perhaps it's not possible to do that for all queries?

> Pagination with Oracle ROWNUM is sub-optimal
> --------------------------------------------
>
>                 Key: HHH-3325
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3325
>             Project: Hibernate Core
>          Issue Type: Bug
>    Affects Versions: 3.2.5
>            Reporter: e. wernli
>         Attachments: OracleLimit.patch
>
>
> Pagination with Oracle ROWNUM is sub-optimal
> The feature works but result in sub-optimal SQL. The generated SQL is the following:
> select * from ( select row_.*, rownum rownum_ from ( select this_.id as id3_0_, this_.version as version3_0_, this_.name as name3_0_, this_.type as type3_0_, this_.marketstatus as marketst5_3_0_ from Customer this_ order by this_.id asc ) row_ ) where rownum_ <= ? and rownum_ > ?
> But this SQL is faster:
> SELECT *
>   FROM (SELECT row_.*, ROWNUM rownum_
>           FROM (SELECT   this_.ID AS id3_0_, this_.VERSION AS version3_0_,
>                          this_.NAME AS name3_0_, this_.TYPE AS type3_0_,
>                          this_.marketstatus AS marketst5_3_0_
>                     FROM customer this_
>                 ORDER BY this_.ID ASC) row_
>          WHERE ROWNUM <= ?)
>  WHERE rownum_ > ?
> The second solution allows Oracle to use an optimization that can dramatically reduce the time of the query, especially one of the first page is retrieved.
> See this link for an explanation of this optimization: http://decipherinfosys.wordpress.com/2007/08/09/paging-and-countstopkey-optimization/

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