RE: Write cache rate

I have many machines running with write caching rates in that region. I have observed that the write caching rate is often low when there is a small proportion of write activity. I use Art Kagel's BR, BTR, and RAU calculations to tune the number of BUFFERS. But I think your RA_PAGES does look high. But Art's calculations will show you that. Regards Malcolm -----Original Message----- From: owner-informix-list@iiug.org [mailto:owner-informix-list@iiug.org] On Behalf Of Doug Conrey Sent: 30 November 2005 15:02 To: informix-list@iiug.org Subject: Write cache rate I have a question about tuning the write cache %. I have an OLTP database running IDS 9.40 on AIX 5.2. There are 300,000 buffers configured (about 30% of physical memory -- 4 GB), and the read cache rate is pretty consistently 98.5 - 99.0%, but the write cache rate hovers between 70 and 75%, which seems low to me. Since this is a sensitive server, I don't want to twiddle settings that are unlikely to help. I'm not sure it's a good idea to just throw more buffers at the thing, since it's got lots. I didn't configure the server, so I'm not certain what the thinking was behind some of the configurations. I do see that the RA_PAGES is set to 1520, which seems pretty likely to push things out. What is the most likely way to improve the write performance? I feel like the read-ahead is pulling too much data (though onstat -p shows it to be using nearly all of it). Is there another setting likely to improve this? Thanks. DC sending to informix-list sending to informix-list