Its more the practice than the actual suggestions.
you need to treat the cause not just the symptoms. what problems are they trying to solve?
well, if the vendor is sure that those settings help them in upgrade/migration due to their past experience, that fine as long as they have tested it and done it a few times with success.
with 20 DBWrs, you have more working sets and more latches protecting the structures. the no.of buffers that each DBWR has to "manage" is lesser when you have more working sets (or DBWRs).
our applications constantly generates around writes of 200 MB/second and reads that are more than that. i only ever use 2 DBWRs. i have previously tried 4, 8, 16 and 20 DBWRs. nothing changed significantly in the performance of the "complete" application. maybe i saved 20-35 seconds somewhere...but thats not my concern.
You can dig deep and produce a table that "could" time the writes with different no. of writers, but does that affect your total/overall response time? how much difference does it make?
if you find that your application needs and uses 4 DBWRs well, then you try and use it. see how fast the writes are compared to 2 DBWRs....what is the delta change?
again, as far as the other settings are concerned, i wouldn't fiddle with them unless i know exactly what i am doing.
Anand do you know what side effects can excessive DBWR cause?
I dont know because I cant find anything which tells you the side effects :-(
On 9/6/06, Anand Rao <panandrao@xxxxxxxxx> wrote: > > 20 DB Writers is way too high. > > what kind of an application is this? Even for a > 'write-only-will-not-select-any-data' application, 20 is high questionable. > > normally, you don't need to dab around with those parameters. why did > they need to be changed? > > sorry, but your Oracle consultant has got it wrong. > > cheers > anand > > > > On 06/09/06, K Gopalakrishnan < kaygopal@xxxxxxxxx> wrote: > > > > Alex, > > > > Did you get an explanation for those suggestions? It would be > > difficult for us to comment on those changes without any additional > > details.. > > > > However, However,However, 20 DBWriters are certainly high for your > > configuration ;) > > > > Have a nice day !! > > ------------------------------------------------------------ > > Best Regards, > > K Gopalakrishnan, > > Co-Author: Oracle Wait Interface: Oracle Press 2004. > > http://www.amazon.com/gp/product/007222729X/ > > > > Coming Soon: Oracle RAC Handbook, Oracle Press 2006 > > http://www.amazon.com/gp/product/007146509X/ > > > > ----- Original Message ---- > > From: amonte <ax.mount@xxxxxxxxx> > > To: oracle-l@xxxxxxxxxxxxx > > Sent: Wednesday, September 6, 2006 1:39:51 AM > > Subject: excessive number of db writer > > > > Hi > > > > I have been suggested by some Oracle Consultant to set 20 Database > > Writer in a 12 CPU HP-UX Server. > > > > Does anyone know what are the side effects of having excessive DBWR? I > > detected a higher CPU usage (between, 1% to 2%) not sure if its due to the > > number of Database Writer. Because when I increased the number of DBWR at > > init.ora I also changed these parameters > > > > _row_cache_cursors = 60 > > _kgl_latch_count = 59 > > _kghdsidx_count = 4 > > statistics_level = basic > > > > again suugested by this guy. > > > > TIA > > > > Alex > > > > > > > > > -- > All I need to make a comedy is a park, a policeman and a pretty girl - > Charlie Chaplin >
-- All I need to make a comedy is a park, a policeman and a pretty girl - Charlie Chaplin