Re: Performance tuning question

> isweb01# vmstat 10
> procs memory page disks faults
> cpu
> r b w avm fre flt re pi po fr sr ad4 ad6 in sy cs us
> sy id
> 1 0 0 648368 47052 10322 0 0 0 7505 136 0 0 839 6241 2114
> 18 10 71
> 1 0 0 651392 42464 9823 0 0 0 6624 0 0 0 667 5374 1703
> 16 10 73
> 0 0 0 648368 42316 9672 0 0 0 6677 0 0 0 652 5290 1674
> 16 10 74
> 1 0 0 650300 39840 6843 0 0 0 4695 0 0 0 866 6123 2217
> 15 10 76
> 0 0 0 648388 39540 6913 0 0 0 4808 0 0 0 1279 9694 3367
> 18 10 72
> 1 0 0 649764 36780 10528 0 0 0 7337 0 0 0 1182 9207 3127
> 23 11 66
> 1 0 0 651372 33180 13763 0 0 0 9392 0 0 0 1129 9458 2950
> 26 13 61
> 1 0 0 651452 57444 14711 0 0 0 10087 666 0 0 889 8044 2315
> 23 13 63
> 1 0 0 650664 55956 12388 0 0 0 8479 0 0 0 773 6791 2006
> 20 11 68
> 2 0 0 649632 55152 10621 0 0 0 7256 0 0 0 805 5811 1985
> 18 11 71
>
> I have increased the shared memory by 50%, and temp_buffers to 5000, but
> no noticeable difference in speed.
> As I mentioned, the system has 2 drives in RAID-1, so pg_xlog is on the
> same disk.
> Would moving pg_xlog to a different disk increase the performance?
> The server I am currently running this on is a temporary server while I
> rebuild our main data server which is SCSI.
> Right now I am going to test a few things on a secondary dev server I
> set (old server with IDE). This one has 2 drives, so I will run some
> tests with pg_xlog on the same drive and on a separate drive.

Having pg_xlog on another disk than the data itselft helps a lot for
frequent writes/updates.

Still it's not so clear to me on *where* exactly your performance
problem is. Is it that 40 msec time you mentioned? On *average* your
machine doesn't seem to be overloaded at all from reading vmstat's
output. Do you need do have this call terminate in less than 40 msec,
even though average load is no problem? Then you have a responsivness
problem, and not an easy one, I'm afraid :/
FreeBSD (or Linux) are not real time systems that can guarantee they
will complete something within msecs.

If this is the case (and I'm a bit guessing here), I'm afraid you need
to buffer data in the client.

> Also, I
> will load the data on an empty database as well as a restored database.
>
> I really need to find a way to make this faster :( The monitoring agent
> which we use has a single logging thread, and if the database does not
> keep up with it it will stall.

Does it buffer at all?

> Worst case, I will virtualize the monitroing agent, but that will
> require quite a bit of work on our side.

Bye, Chris.

--

Chris Mair
http://www.1006.org