Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp> writes:
> I have made a new version of pgbench which allows not to update
> branches and tellers tables, which should significantly reduce the
> contentions.
I used this version of pgbench in some fresh runs on RedHat's 4-way SMP
Linux box. I did several test runs under varying conditions (pgbench
scale 500 or 50, checkpoint_segments/wal_files either default 3/0 or
30/5, fsync on or off). I compared current CVS tip (including the
now-committed lwlock rev 2 patch) to 7.1.3. The results are attached.
As you can see, current beats 7.1 pretty much across the board on that
hardware. The reason seems to be revealed by looking at vmstat output.
Typical "vmstat 5" output for 7.1.3 (here in a 6-client pgbench -N
run) is
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
1 0 0 0 108444 8920 4917092 0 0 213 0 170 4814 0 1 99
1 0 0 0 103592 8948 4921912 0 0 234 357 230 4811 1 1 98
0 0 0 0 98776 8968 4926704 0 0 233 428 235 4854 1 1 97
0 0 0 0 94300 8980 4931168 0 0 216 423 229 4809 1 2 97
0 0 0 0 89960 8984 4935504 0 0 209 771 421 4723 2 2 96
0 0 0 0 69280 9016 4956140 0 0 205 842 457 4645 1 2 96
The system is capable of much greater I/O rates, so neither disks nor
CPUs are exactly exerting themselves here. In contrast, 7.2 shows:
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
2 0 0 0 2927344 9148 1969356 0 0 0 5772 102 13753 61 32 7
7 0 0 0 3042272 9148 1969716 0 0 0 2267 2400 14083 58 32 10
5 0 0 0 3042168 9148 1970100 0 0 0 2734 1028 12994 53 37 11
I think that 7.1's poor showing here is undoubtedly due to the spinlock
backoff algorithm it used --- there is no other way to explain 99% idle
CPU than that all of the backends are caught in 10-msec select() waits.
> With the new pgbench, I ran a test with current and 7.1 and saw
> not-so-small differences. Any idea to get better performance on 7.2
> and AIX 5L combo?
I'm thinking more and more that there must be something weird about the
cs() routine that we use for spinlocks on AIX. Could someone dig into
that and find exactly what it does and whether it's got any performance
issues?
regards, tom lane
