Ron wrote:
If I understand your HW config correctly, all of the pg stuff is on the
same RAID 10 set?
No, the system and the WAL are on a RAID 1 array and the data on their
own RAID 10 array.
As I said earlier, there's only a few writes in the database so I'm not
really sure the WAL can be a limitation: IIRC, it's only used for writes
isn't it?
Don't you think we should have some io wait if the database was waiting
for the WAL? We _never_ have any io wait on this server but our CPUs are
still 30-40% idle.
A typical top we have on this server is:
15:22:39 up 24 days, 13:30, 2 users, load average: 3.86, 3.96, 3.99
156 processes: 153 sleeping, 3 running, 0 zombie, 0 stopped
CPU states: cpu user nice system irq softirq iowait idle
total 50.6% 0.0% 4.7% 0.0% 0.6% 0.0% 43.8%
cpu00 47.4% 0.0% 3.1% 0.3% 1.5% 0.0% 47.4%
cpu01 43.7% 0.0% 3.7% 0.0% 0.5% 0.0% 51.8%
cpu02 58.9% 0.0% 7.7% 0.0% 0.1% 0.0% 33.0%
cpu03 52.5% 0.0% 4.1% 0.0% 0.1% 0.0% 43.0%
Mem: 3857224k av, 3307416k used, 549808k free, 0k shrd, 80640k
buff
2224424k actv, 482552k in_d, 49416k in_c
Swap: 4281272k av, 10032k used, 4271240k free 2602424k
cached
As you can see, we don't swap, we have free memory, we have all our data
cached (our database size is 1.5 GB).
Context switch are between 10,000 and 20,000 per seconds.
This concept works for other tables as well. If you have a tables that
both want services at the same time, disk arm contention will drag
performance into the floor when they are on the same HW set.
Profile your HD access and put tables that want to be accessed at the
same time on different HD sets. Even if you have to buy more HW to do it.
I use iostat and I can only see a little write activity and no read
activity on both raid arrays.
--
Guillaume
