Re: Performance DB-Link

good point on being aware of the rollback segments, but here's a little clarification

a select doesn't generate rollback in and of itself, however it may refrence rollback segment entries for read-consistency. however, this will all occur on the node where the table resides, so there should be no issue with db links

also to be considered are the potential for temp segments for disk-based sorts (which are sometimes needed for joins) -- these will be created on the node where the sort is processed, as i recall oracle may join tables on a remote node before returning the results

regarding ROLLBACK/COMMIT there is a gotcha with db links -- db links and read-only databases do not mix, you'll get an ORA-16000. as i recall we got this trying to select over a db link FROM a read-only database, it may work linking to a read-only database, but it may not

"NetComrade" <andreyNSPAM_at_bookexchange.net> wrote in message news:3fa12984.521557740_at_nyc.news.speakeasy.net...
> Few warnings
>
> Tune any query doing joins (explain plans) over the link
> Be aware that even a SELECT uses rollback segment, which means any
> transaction over the link will require a rollback or commit at some
> point, or all your RBS will stop being usable at some point
> If you do queries over the link, try not do do joins of multiple
> tables on the other end, as Oracle doesn't lookups for each remote
> object involved in your query.
>
> If you're using db_links just for replication, i think it's fine.
> Production queries, require a close look.
>
> On 29 Oct 2003 05:11:25 -0800, sceddie_at_gmx.de (Arne Bippes) wrote:
>
> >Hi,
> >
> >we are thinking about using Oracles DB_link feature to connect two
> >Databases.
> >Currently the data is transported via MQSeries.
> >
> >Does anybody have any experience about the Performance. Do I have to
> >expect increased or decreased Performance?
> >
> >Greetings
> >
> >Arne Bippes
>
> .......
> We use Oracle 8.1.7.4 on Solaris 2.7 boxes
> remove NSPAM to email
Received on Thu Oct 30 2003 - 10:14:18 CST