Date: Sun, 4 Apr 1999 23:09:28 -0700 (PDT) From: Tom <tom@uniserve.com> To: Ilya Obshadko <ilya@zhurnal.ru> Cc: freebsd-stable@freebsd.org Subject: Re: Poor SMP performance Message-ID: <Pine.BSF.4.02A.9904042304210.22567-100000@shell.uniserve.ca> In-Reply-To: <5400.990405@zhurnal.ru>
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On Mon, 5 Apr 1999, Ilya Obshadko wrote: > Hello, > > Few days ago I wrote to mysql mail list about poor performance on > FreeBSD/SMP (Dual P-II 333, UW SCSI, 256M). Here is the answer I got: > > > The problem is related to SMP in FreeBSD. Because a database > > server is I/O bound, and FreeBSD's SMP implementation does a giant > > i/o lock around the kernel for each processor, it actually > > is SLOWER to run MySQL on a dual processor FreeBSD machine than > > on a single processor. I ran into the same problem -- had just > > bought a dual pII 350, which then became my workstation machine > > when MySQL ran slowly on it. > > > > The GOOD NEWS is that, on a single processor 450MHZ machine, I found > > FreeBSD MySQL to run significantly FASTER than the benchmarks for any Linux > > box, including dual PIIs. > > Any comments about it? It is worse than that. mysql only allows a single writer. If you are doing a lot of UPDATEs and INSERTs, only one thread at a time can actually run. OSes that schedule hreads that over multiple CPUs only improve mysql's SELECT performance. Now, if you database really is IO bound, it doesn't matter what OS you us, as SMP will not help. Small databases may be mostly cached, or you IO subsystem may be really last, for example. The latter is very important for any database system. > Best regards, > Ilya mailto:ilya@zhurnal.ru Tom To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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