Re: Oracle 9i Latching Issue

Johne_uk <edgarj_at_tiscali.co.uk> wrote in news:412ea049-3b68-4126-a1ad- f7c5b6379c6d_at_s13g2000prd.googlegroups.com:

> Hi,
>
> I'm a beginner Oracle DBA who is facing a performance issues on a 9i
> instance running on Solaris. The db
> instance hosts a number of web applications including in-house apps
> and oracle apps such as Discoverer.
>
> For the past month there have been periods where the db has slowed
> down to an almost unusable state. I've
> looked at various options including reusable sql in the shared pool
> etc but, using statspack, I've finally manged to find a corellation
> whereby during slow periods the latch free waits % increases
> dramatically.
>
> As there are a multitude of apps running from this instance I need to
> try and pinpoint whichs app(s) are generating the latch free waits.
>
> My findings. When all is well my Latch Hit % is 99.xx which is normal.
> During slowdown earlier today this dropped down to 85% indicating an
> issue.
>
> Digging deeper into this the primary culprit for this latch activity
> seems to be with cache buffer chain latches which were experiencing a
> 25% miss rate.
>
> Once the db speeded up latches reverted back to being insignificant.
> My suspicion is that the issue is being
> caused by Discoverer sessions as the sessions always features
> predominantly in statspack ouput with large
> volumes of buffer gets during slowdown.
>
> However, what I now need is some input as regards how to find the
> offending sessions that are causing these
> excessive latch waits times. I'd appreciate some assistance from the
> user community on this as I'm on a steep
> learning curve for my experience level.
>
> It would almost be impossible to rewrite the sql in any apps but I may
> have the option to remove any offending
> apps to another db server as opposed to our primary prod instance.
>
> It should also be pointed out that the issue is not caused by rogue
> sessions thrashing the db, as activity can be minimal during slowdown.
>
> Thanks in anticipation
> John
>

Database are not slow.
SQL statements are slow.
Identify the slow SQL using SQL_TRACE & make them faster. Received on Fri Mar 28 2008 - 08:36:13 CDT