Re: DB WR PERFORMANCE ON I/O!!!!!!

This is an issue that always haunts people but some people don't know it. There could be 2 problems here:
1) you checkpoint every 3 seconds (but I don't believe that). So making your redo log file bigger won't help
(I assume that you have checked the checkpoints).

2) the dbwr wakes up every 3 second (this is the idle loop for the DBWR). Then there are some possibilies here:

1. your write batch size is too large (db_files * db_file_simultaneous_writes)/2 if this is too large we could write many blocks at the same time. And then you could run into problem b:
2. Your I/O is not spread correctly over all your disks, causing one of your disks to become hot. e.g. if the write batch is 128 and you write to 2 disks then each disk should handle on avg. 64 writes.

but all this said, you say that there are no reads in the database, then the DBWR performance shouldn't/can't really impact the performance of the foreground. If the foregrounds would do reads they will suffer from the burts of writes. However if no reads happen, they can't suffer.

so you may have problem, but it may not be related to the DBWR ......

Fun he !

Anjo.

naveen_arora_at_my-deja.com wrote:

> Hi,
> I am using Oracle 7.3.3 on unix for a real time system.
> The application mostly involves lot of updates.
> The whole table is in memory and no physical read is there.
> But I/O is hogging resources as db wr always writes after 3 seconds.
> i want to increase this interval or have some get around.
> The platform i am using is fully fault-tolerant so the
> chance of going down is extreamly low.
> If dbwr writes less frequently the I/O will be better.
> Thanks for any help.
> Naveen
> naveen_at_cdotd.ernet.in
>
> Sent via Deja.com http://www.deja.com/
> Share what you know. Learn what you don't.
Received on Fri Jul 23 1999 - 04:14:01 CDT