Josh Chamas
Mon, 02 Feb 2004 15:30:25 -0800
I've been monitoring the disk usage in my StateDir for some time now and I've found rather interesting stuff about it.
First the basics: it's an nfs shared statedir, used by four web servers. I'm using a ramdisk for it, since using an actual disk for it proved discouraging.
Here are the stats: measuring from 30.1.2004 – 18:25:00 to 2.2.2004 – 20:32:00 number of disk writes:9728300 number of disk reads : 100310
I can't imagine that these performance metrics are measuring what you think they are. There is no way that there is a 97/1 write/read ratio.
I would consider that your mirrored situation might be buffering/caching reads locally, and only writing through, so you only see a small fraction of reads. I don't really know enough about the mirroring technologies you are using to suggest more, but certainly these numbers are pretty suspicious.
Any idea why things are the way they are and what could/should be done ?
If you want to get to how an Apache::ASP process does its read/writes to the MLDBM::Sync databases, I would fire up the apache web server under httpd -X mode ( for apache 1.3.2x ), while running under strace capturing the system calls that you are interested in. This assumes you are using linux, but I am sure there are other system call trace utilities for your OS. This would help isolate the stats from the web server side, vs. stats that are particular to your clustering/mirroring software.
________________________________________________________________ Josh Chamas, Founder phone:925-552-0128 Chamas Enterprises Inc. http://www.chamas.com NodeWorks Link Checker http://www.nodeworks.com
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