openjpa-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Milosz Tylenda (JIRA)" <>
Subject [jira] Updated: (OPENJPA-759) Query pagination on DB2 - an alternative way
Date Fri, 31 Oct 2008 18:05:44 GMT


Milosz Tylenda updated OPENJPA-759:


> Query pagination on DB2 - an alternative way
> --------------------------------------------
>                 Key: OPENJPA-759
>                 URL:
>             Project: OpenJPA
>          Issue Type: Improvement
>          Components: sql
>    Affects Versions: 2.0.0
>         Environment: DB2 UDB
>            Reporter: Milosz Tylenda
>            Priority: Minor
>         Attachments:, OPENJPA-759.patch,
> The attached patch provides an alternative way of doing paging in DB2.
> I made it hoping that it would improve the performance of paging queries
> but it didn't, at least not when the database and OpenJPA are co-located.
> There is probably no point in committing this patch unless someone
> proves it gives any advantages.
> I am however presenting it here, maybe some users will find it useful
> (it would be nice if someone could check timings with remote database).
> Attached are:
> - a patch which modifies DB2Dictionary and also adds a few tests to TestQueryPagination.
> - a standalone modified DB2Dictionary class.
> - a timer program which was supposed to prove the superior performance but failed :)
> Some characteristics:
> - The idea is to limit the result set returned by SQL query instead of skipping rows
>   when traversing the result set in OpenJPA. A similar approach exists
>   in OracleDictionary.
> - If setMaxResulsts and setFirstResult were called on Query, the SQL query
>   [QUERY] is modified as follows:
>     [QUERY]
>   ) AS rr
> ) AS r WHERE rn > [n] ORDER BY rn
> - The modified SQL query adds one column to the end of column list in the
>   result set. Luckily, I couldn't find any side effects of doing this.
> - If only setMaxResults was called on Query, only FETCH FIRST [m] ROWS ONLY
>   is appended to SQL query - this is how it works currently.
> - The new way of paging will be used only if the database is a UDB 8.1 or later
>   because of ORDER OF construct and FETCH FIRST [m] ROWS ONLY in a subselect.
>   Maybe some other DB2 flavours could also handle it but I have no access.
> - User can fall back to the old behaviour by setting supportsSelectStartIndex
>   Dictionary property to false.

This message is automatically generated by JIRA.
You can reply to this email to add a comment to the issue online.

View raw message