Re: pg 8.1.3, AIX, huge box, painfully slow.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Luke Lonergan" <llonergan(at)greenplum(dot)com>
Cc: "Gavin Hamill" <gdh(at)laterooms(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: pg 8.1.3, AIX, huge box, painfully slow.
Date: 2006-04-07 22:02:55
Message-ID: 17108.1144447375@sss.pgh.pa.us
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"Luke Lonergan" <llonergan(at)greenplum(dot)com> writes:
> That said, I find typical memory bandwidth for the P4 in applications is
> limited at about 2GB/s. See here for more detail:
> http://www.cs.virginia.edu/stream/standard/Bandwidth.html

> In fact, looking at the results there, the IBM 650m2 only gets 6GB/s
> on all 8 CPUs. I wouldn't be surprised if the strange L3 cache
> architecture of the IBM 650 is holding it back from streaming memory
> access efficiently.

Given Gavin's latest report, I'm wondering how much the IBM slows down
when a spinlock operation is involved. If the memory architecture isn't
good about supporting serialized access to memory, that gaudy sounding
bandwidth number might have little to do with PG's real-world behavior.
On the other hand, we already know that Xeons suck about as badly as
can be on that same measure; could the pSeries really be worse?

regards, tom lane

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