[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3325) Pagination with Oracle ROWNUM is sub-optimal
Christian Daszenies (JIRA)
noreply at atlassian.com
Thu Jun 24 04:11:09 EDT 2010
[ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=37558#action_37558 ]
Christian Daszenies commented on HHH-3325:
------------------------------------------
The proposed patch uses the query hint {{select /*+ FIRST_ROWS\(n\) */ ...}}. This would not work as expected as _n_ is a variable ("where n is any positive integer") as stated in oracle docs:
http://download.oracle.com/docs/cd/A97630_01/server.920/a96533/hintsref.htm
The challenge is to determine an appropriate value in the dialect implementation.
> 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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