From: Thor Newman (Thor@airg.com)
Date: Wed Jun 23 2004 - 19:32:11 EDT
Hello Managers,
I am in what I assume to be the somewhat classic dilemma of DSR vs
Memory Interleave...
The system is a beauty, a Sun refurbished Enterprise 4500 with 8x400 Mhz
processors (8MB cache) and 8GB of identical RAM evenly spread across the
4 boards -- 8-way Interleave is possible, OS is Solaris 9. It's a
production database platform, and will be running MySQL 4.0 (SPARC
64-bit version).
I am finding it surprisingly difficult to nail down anything concrete
with regards to the performance hit and general negative consequences of
disabling memory interleave. Sun recommends leaving it on 'unless' DSR
needs to be enabled and generally seems studiously neutral on the
matter.
One nugget I was told (which I don't believe to be correct) is that
disabling memory interleave chops up the RAM into isolated pools and
that CPU's on board 0 say can only access RAM on board 0 with interleave
disabled. Again I do not believe this is the case, I understand memory
interleaving to be about increasing overall bandwidth and reducing
latency by performing RAM operations in parallel, not changing what is
actually addressable and usable by a given processor. Can someone please
confirm or deny this?
Second thing, is the performance hit likely to be significant? I am
inclined to go with the DSR overall as I don't expect disabling
interleaving to have too much of an impact in the grand scheme of things
on an 8GB system: IO and then CPU resources are likely to be a
bottleneck first is my feeling.
I have seen numbers ranging from 1%-5% floating around the ether in
terms of a performance penalty, but Sun doesn't seem to commit itself to
anything 'official'. Any opinions/recommendations from this list will be
carefully reviewed and much appreciated.
Thank-you
Thor Newman
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