Re: 7.1 vs. 7.2 on AIX 5L - Mailing list pgsql-hackers

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
>