Date: Tue, 01 Jan 2008 05:04:56 +0100 From: Kris Kennaway <kris@FreeBSD.org> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-performance@freebsd.org Subject: Re: mysql scaling questions Message-ID: <4779BBE8.2050608@FreeBSD.org> In-Reply-To: <flb6bp$8kq$1@ger.gmane.org> References: <20071201205609.GA54238@harmless.hu> <200712012108.lB1L8qAd005766@lava.sentex.ca> <20071201211012.GA55519@harmless.hu> <20071201122122.S884@192.168.1.107> <20071204130810.GA77186@harmless.hu> <47779AA7.2060801@FreeBSD.org> <20071230132451.GA61295@harmless.hu> <47779EBC.5020900@FreeBSD.org> <20071230134354.GA63555@harmless.hu> <4777A65C.8020406@FreeBSD.org> <20071230141118.GA67574@harmless.hu> <4777AB9C.1010003@FreeBSD.org> <flb6bp$8kq$1@ger.gmane.org>
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Ivan Voras wrote: > Kris Kennaway wrote: >> Gergely CZUCZY wrote: > >>>> It looks like myisam is doing huge numbers of concurrent reads of the >>>> same file which is running into exclusive locking in the kernel >>>> (vnode interlock and lockbuilder mtxpool). Does it not do any >>>> caching of the data in userspace but relies on querying into the >>>> kernel every time? innodb doesn't have this behaviour. >>> Sorry, but was this a rethorical kind of question, or was this >>> addressed to me? :) >>> If the later, then how do I find this out? >> It's a general question. It looks like myisam either has a design >> deficiency in this regard or it has poor defaults. If it can be made to >> improve caching of the data in userland then performance should improve. > > Isn't this common for software developed for Linux? I mean assuming > syscalls are cheap; for example: gettimeofday(2), settitle(2), etc. I > don't think the applications should be blamed for relying on performance > optimizations not present in FreeBSD. Saying applications must do their > own caching instead of relying on the kernel and need to avoid > concurrent accesses to the same file seems like a doctrine from the dark > ages. Why? Even if Linux magically has faster syscalls somehow, they are still not zero cost so avoiding huge numbers of unnecessary trips into the kernel is in no sense a "doctrine from the dark ages". Besides, if my hypothesis about the problem is correct then mysql itself does this with the alternate innodb backend anyway. Krishome | help
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