RAID-0
And how many drives?
Just two.
We have an application server that is processing requests. Each request consists of a combination of selects, inserts, and deletes. We actually see degredation when we get more than 40 concurrent requests. The exact number of queries executed by each request isn't known. It varies per request. But, an example request would be about 16 inserts and 113 selects. Any given request can't execute more than a single query at a time.
avg-cpu: %user %nice %system %iowait %steal %idle
34.29 0.00 7.09 0.03 0.00 58.58
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 112.20 0.00 133.40 0.00 1964.80 14.73 0.42 3.17 0.04 0.48
The iowait seems pretty low, doesn't it?
Yes, but you are issuing 133 write operations per seconds per drive(s) - this is nearly the limit of what you can get with 15k RPM drives (actually, the limit should be somewhere around 200..250 IOPS but 133 isn't that far).
As you mentioned in a separate response, we have fsync shut off. Regardless, we shut off a lot of logging in our app and reduced that number to approx 20 per second. So, a lot of those writes were coming from outside the db. We do a lot of logging. We should consider turning some off, it seems.
top - 10:11:43 up 12 days, 20:48, 6 users, load average: 10.48, 4.16, 2.83
Tasks: 798 total, 8 running, 790 sleeping, 0 stopped, 0 zombie
Cpu0 : 33.3%us, 7.6%sy, 0.0%ni, 59.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Each of the 256 requests was being processed by a php process. So, it could certainly be faster. But, the fact that we're seeing the db performance degrade would seem to indicate that our application is fast enough to punish the db. Isn't that true?
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