From: Tim Chipman (chipman@ecopiabio.com)
Date: Mon Nov 04 2002 - 16:56:42 EST
Hi Folks,
A general question in two parts, on the same theme. I'm hoping to elicit
comments from people who have actually done scaling "in this kind of
way", in particular (ideally) on DataBase (oracle, etc) server
environments, but really, anything with a mix of CPU and IO would be
comparable for my purposes probably. In all cases I'm assuming that I/O
is *not* the primary bottleneck, ie, that CPU usage is more of a
bottleneck than I/O (although clearly both are related to performance in
this sort of environment).
Part:1:
-> assume you scale a DB server from a quad-CPU-UltraSparc-II/450mhz
(e450 calibre box) to a dual-CPU-UltraSparc-III/900mhz (v480 or v880
calibre box), and given the (apparently more-or-less true?) assumption
that performance for US-III CPUs is a fairly linear scale-up when
compared to US-II CPUs,
-do we expect performance to be faster on the 900mhz CPU system, since a
given (unit of work for single unthreaded process) can be ~2x greater
for a 900 vs 450mhz CPU?
-do we expect greater capacity for multiple parallel independant
processes on the quad-cpu machine, since there are physically more CPUs
available to do work at any given instant? (or, does task scheduling
more-or-less render this transparent / irrelevant? Is there "more
overhead" to process/thread management on SMP systems with more CPUs, or
is this more-or-less constant overhead? Linear overhead scaling with CPU
count?)
Part:2: (more blasphemous in nature :-)
-> Assume:
--you have no issues with (stability, hardware selection, maintenance,
support) of linux on reliable, "high performance" X86 hardware (ie,
dual-athlon-MP @ 1800 mhz/"2200+"CPU, Ultra-160 SCSI-64-bit PCI disk
subsystem//10k RPM SCSI drives, quality DDR ECC 266 ram, etc, no
bleeding edge features in OS/solid kernel)
--hence no trouble with > 300 day uptimes on such a platform, and then,
downtime is only for scheduled maintenance,
--*given* a knowledge that approximately, for *purely* CPU-limited
performance, athlon "true MHZ" is approximately equal to UltraSparc II
CPU performance (when compared to CPUs of either e450 or e3500 server)
[this has been true for tests I have performed, BTW, as I said such a
case where IO is not an issue and CPU is the bottleneck - thus, a
dual-athlon-1600mhz performs on par for CPU-limited task ~identically to
an 8-CPU e3500 with 400mhz CPUs, or ~2x faster than a 4-cpu@400mhz e450]
Then,
--> do we expect the answers from (Part:1:) above regarding
quad-slow-CPU to dual-faster-CPU scaling of a server platform to have
any relevance?
--> has anyone actually migrated a production database from e450 calibre
(quad-450 UltraSparc II) gear over to (linux X86 Dual CPU gear as
described) and found the performance to scale (poorly / decently /
nicely?)
Clearly, I realize that there are *tons* of variables when attempting to
compare (1) Sparc SMP based on UltraSparc II vs UltraSparc III CPUs, (2)
UltraSparc of any kind vs. X86 CPU/Hardware platform (ie, CPU cache,
data bus, etc) (3) Solaris vs Linux OS platform issues. However, in
part, I'm hoping to elicit comments in these veins from people who have
actual experience with such a migration / with similar server
functionality on the different platforms discussed here.
Also, clearly, I realize that X86 gear is NOT as scalable for a pure-MP
system as UltraSparc-based equipment; however, this isn't my concern,
especially since (last time I was aware?) the bulk of functionality
served by Sun/UltraSparc based gear is NOT in 16-CPU (and up) MP boxes
but rather in (gasp! single), dual, or quad CPU -based systems.
Any comments or feedback regarding these questions are certainly very
much appreciated. As always, I'll summarize to the list.
Thanks!
Tim Chipman
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