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

Are you trying to improve write cache rate (how much I write) or write performance (how fast I write it)? To improve the write cache rate you need to reduce the number of pages you are writing. Either a) write less row data... Are you updating columns or rows you do not need to update? b) write less pages For rows you are writing pull the least used columns into another table. So you write less wide rows since you are getting more rows per page. This applies to inserts as well as updates/deletes. Do you have indexes that cover other indexes? Index on column a and an Index on columns a,b OR Index on columns a,b and an index on columns a,b,c In both cases the first index is not needed. You need to get IDS Well are transactions updating columns they do not need to? Can you build a cluster index on tables