Chris Mair wrote:
Hi,
I've got a somewhat puzzling performance problem here.
I'm trying to do a few tests with PostgreSQL 8.1.3 under Solaris
(an OS I'm sort of a newbie in).
The machine is a X4100 and the OS is Solaris 10 1/06 fresh install
according to manual. It's got two SAS disks in RAID 1, 4GB of RAM.
Now the problem is: this box is *much* slower than I expect.
I've got a libpg test program that happily inserts data
using PQputCopyData().
It performs an order of magnitude worse than the same thing
on a small Sun (Ultra20) running Linux. Or 4 times slower than
an iBook (sic!) running MacOS X.
So, I've this very bad feeling that there is something basic
I'm missing here.
Following are some stats:
"sync; dd; sync" show these disks write at 53 MB/s => good.
iostat 1 while my test is running says:
tty sd0 sd1 sd2 sd5
cpu
tin tout kps tps serv kps tps serv kps tps serv kps tps serv us sy
wt id
1 57 0 0 0 0 0 0 0 0 0 1809 23 70 0
1 0 99
0 235 0 0 0 0 0 0 0 0 0 2186 223 14 1
1 0 99
0 81 0 0 0 0 0 0 0 0 0 2488 251 13 1
1 0 98
0 81 0 0 0 0 0 0 0 0 0 2296 232 15 1
0 0 99
0 81 0 0 0 0 0 0 0 0 0 2416 166 9 1
0 0 98
0 81 0 0 0 0 0 0 0 0 0 2528 218 14 1
1 0 99
0 81 0 0 0 0 0 0 0 0 0 2272 223 15 1
0 0 99
If I interpret this correctly the disk writes at not more than 2.5
MB/sec while the Opterons do nothing => this is bad.
I've tried both, a hand compile with gcc and the solarispackages
from pgfoundry.org => same result.
Eons ago PCs had those "turbo" switches (it was never totally clear
why they put them there in the first place, anyway). I've this bad
feeling there's a secret "turbo" switch I can't spot hidden somewhere
in Solaris :/
I ran across something like this on a Solaris 8, RAID1 system, and
switching off logging on filesystem containing postgres made a huge
difference!
Now solaris 8 is ancient history, however see:
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6238533
Apparently there can still be issues with logging without forcedirectio
(which is the default I think).
I suspect that making a *separate* filesystem for the pg_xlog directory
and mounting that logging + forcedirectio would be a nice way to also
get performance while keeping the advantages of logging + file
buffercache for the *rest* of the postgres components.
Cheers
Mark
