Re: pg_dump & performance degradation

At 06:05 1/08/00 -0700, Don Baccus wrote:
>At 02:31 PM 8/1/00 +1000, Philip Warner wrote:
>
>>>Have you tried pg_dump on a multi-processor machine, which most serious
>>>database-backed websites run on these days? Do you see the same
>performance
>>>degradation? My site runs on a dual P450 with RAID 1 LVD disks, and cost
>>>me exactly $2100 to build (would've been less if I'd laid off the extra
>>>cooling fans!)
>>
>>The original request came from a person with a "4-CPU Xeon with 2GB of
>>RAM", but the "solution" does not seem to work for them (I think), so it's
>>probably a waste of time.
>
>It seems really strange that pg_dump could suck the guts out of a
>four-processor
>machine. What kind of device were they backing up to? Disk?

I *think* you missed the point; the problem is that the CPU is perfectly
adequate to "suck the guts" out of his disks. If it was just a CPU issue,
then 'nice' would work.

The throttle stuff is there to slow down pg_dump and thereby reduce IO
load. AFAIK, there is no supported way of limiting IO demand in Unix. But
I'd love to be corrected. My meagre PIII 550 is perfectly able to simulate
the problem (with just a million rows) - and the code seems to help. But
not apparently for the 4-CPU Xeon (although I don't think he has tested the
most recent code).

But, given the negative response to the code (and the fact that it seems to
only be somewhat effective), I'll probably be ditching it.

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