Re: Amazon EC2 CPU Utilization - Mailing list pgsql-general

I have deployed PostgresSQL 8.4.1 on a Fedora 9 c1.xlarge (8x1 cores) instance
in the Amazon E2 Cloud. When I run pgbench in read-only mode (-S) on a small
database, I am unable to peg the CPUs no matter how many clients I throw at it.
In fact, the CPU utilization never drops below 60% idle. I also tried this on
Fedora 12 (kernel 2.6.31) and got the same basic result. What's going on here?
Am I really only utilizing 40% of the CPUs? Is this to be expected on virtual
(xen) instances?

[root@domU-12-31-39-0C-88-C1 ~]# uname -a
Linux domU-12-31-39-0C-88-C1 2.6.21.7-2.ec2.v1.2.fc8xen #1 SMP Fri Nov 20
17:48:28 EST 2009 x86_64 x86_64 x86_64 GNU/Linux

-bash-4.0# pgbench -S -c 16 -T 30 -h domU-12-31-39-0C-88-C1 -U postgres
Password:
starting vacuum...end.
transaction type: SELECT only
scaling factor: 64
query mode: simple
number of clients: 16
duration: 30 s
number of transactions actually processed: 590508
tps = 19663.841772 (including connections establishing)
tps = 19710.041020 (excluding connections establishing)

top - 15:55:05 up  1:33,  2 users,  load average: 2.44, 0.98, 0.44
Tasks: 123 total,  11 running, 112 sleeping,   0 stopped,   0 zombie
Cpu(s): 18.9%us,  8.8%sy,  0.0%ni, 70.6%id,  0.0%wa,  0.0%hi,  1.7%si,  0.0%st
Mem:   7348132k total,  1886912k used,  5461220k free,    34432k buffers
Swap:        0k total,        0k used,        0k free,  1456472k cached

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND


 2834 postgres  15   0  191m  72m  70m S   16  1.0   0:00.66 postmaster


 2838 postgres  15   0  191m  66m  64m R   15  0.9   0:00.62 postmaster


 2847 postgres  15   0  191m  70m  68m S   15  1.0   0:00.59 postmaster


 2837 postgres  15   0  191m  72m  70m S   14  1.0   0:00.47 postmaster


 2842 postgres  15   0  191m  66m  64m R   14  0.9   0:00.48 postmaster


 2835 postgres  15   0  191m  69m  67m S   14  1.0   0:00.54 postmaster


 2839 postgres  15   0  191m  69m  67m R   14  1.0   0:00.60 postmaster


 2840 postgres  15   0  191m  68m  67m R   14  1.0   0:00.58 postmaster


 2833 postgres  15   0  191m  68m  66m R   14  1.0   0:00.50 postmaster


 2845 postgres  15   0  191m  70m  68m R   14  1.0   0:00.50 postmaster


 2846 postgres  15   0  191m  67m  65m R   14  0.9   0:00.51 postmaster


 2836 postgres  15   0  191m  66m  64m S   12  0.9   0:00.43 postmaster


 2844 postgres  15   0  191m  68m  66m R   11  1.0   0:00.40 postmaster


 2841 postgres  15   0  191m  65m  64m R   11  0.9   0:00.43 postmaster


 2832 postgres  15   0  191m  67m  65m S   10  0.9   0:00.38 postmaster


 2843 postgres  15   0  191m  67m  66m S   10  0.9   0:00.43 postmaster



[root@domU-12-31-39-0C-88-C1 ~]# iostat -d 2 -x
Linux 2.6.21.7-2.ec2.v1.2.fc8xen (domU-12-31-39-0C-88-C1)       01/27/10

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz
avgqu-sz   await  svctm  %util
sda1              0.57    15.01    1.32    3.56    34.39   148.57    37.52
0.28   57.35   3.05   1.49
sdb1              0.03   112.38    5.50   12.11    87.98   995.91    61.57
1.88  106.61   2.23   3.93

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz
avgqu-sz   await  svctm  %util
sda1              0.00     0.00    0.00    1.79     0.00    28.57    16.00
0.00    2.00   1.50   0.27
sdb1              0.00     4.46    0.00   14.29     0.00   150.00    10.50
0.37   26.00   2.56   3.66

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz
avgqu-sz   await  svctm  %util
sda1              0.00     0.00    0.00    0.00     0.00     0.00     0.00
0.00    0.00   0.00   0.00
sdb1              0.00     0.00    0.00    0.00     0.00     0.00     0.00
0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz
avgqu-sz   await  svctm  %util
sda1              0.00     3.57    0.00    0.79     0.00    34.92    44.00
0.00    3.00   3.00   0.24
sdb1              0.00     0.00    0.00    0.00     0.00     0.00     0.00
0.00    0.00   0.00   0.00




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