Re: 7.1 vs. 7.2 on AIX 5L

Tom,

Can I use the fourth graph (scale=50, fsync=on) to show how 7.2 could
outperform 7.1 on SMP boxes? I'm going to make a presentation at
Net&Com 2002 (http://expo.nikkeibp.co.jp/netcom/web/e/index.html) the
day after tomorrow.
--
Tatsuo Ishii

> 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
>