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

[Seth Wilcox (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=38792#action_38792 ] 

Seth Wilcox commented on HHH-3325:
----------------------------------

In oracle, to get maximum performance, you can explicitly tell the DB that you are doing a pagination query(by using the  select /*+ FIRST_ROWS(n) */ hint).  When you do this, as soon as oracle has the number of rows you said you needed, the DB immediately stops and returns.  Also, it can change the way the Cost based optimizer works.  In my experience, it makes a noticeable and measurable impact on performance.  The hint is what is still missing.

> 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, 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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