Re: latches: cache buffers chains

You have a good hit ratio, so I personally wouldn't worry too much about it.

One thing to look at is the v$latch_children table for specific latches which individually responsible for misses (see my posts to Ross Mohan on 'an oldie ...'), then track the most expensive latch back to the database block it is protecting.

You can be lucky and change the contention dramatically by changin the number of db block hash buckets so that very commonly used blocks (typically index root blocks) hash to different chains.

Watch out - there are typically db_block_buffers/4 child latches / hash chains.

What is the spin_count ? You can get an idea on how much of your CPU is simply 'lost' in spinning by doubling and halving it, and seeing if this makes any significant difference to the CPU usage and total throughput.

--

Jonathan Lewis
Yet another Oracle-related web site: www.jlcomp.demon.co.uk

chuckh_at_safeplace.net wrote in message <7h9luu$85s$1_at_nnrp1.deja.com>...
>I recently increased the buffer cache size to 300m on a 4 cpu NT Oracle
>database. Since then I've noticed a lot more misses on the "cache
>buffers chains" latch and a sleeps/miss ratio of 73.2%. What can I do
>to reduce the number of misses on the latch and reduce the number of
>sleeps? There seems to be no documentation on tuning this latch.
>
>The hit ratio on it is .997. Should I even be concerned about it?
>
Received on Tue May 11 1999 - 14:50:38 CDT