Date: Fri, 31 Mar 2006 07:50:53 +0200 From: usleepless@gmail.com To: "Bill Moran" <wmoran@collaborativefusion.com> Cc: mmiranda@123.com.sv, freebsd-questions@freebsd.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: terrible performance in 6.1beta4 Message-ID: <c39ec84c0603302150j617fe1ecmd4da92ac1593ae97@mail.gmail.com> In-Reply-To: <20060330192437.043e88ff.wmoran@collaborativefusion.com> References: <442B2FC6.9040001@123.com.sv> <20060330011834.GA84658@xor.obsecurity.org> <c39ec84c0603300047u5530fc1fjb1ba93fcafcd490d@mail.gmail.com> <442BF0BB.8010504@123.com.sv> <c39ec84c0603301141g42f0f367i1c7669c90e1115d7@mail.gmail.com> <20060330202145.GA17856@xor.obsecurity.org> <c39ec84c0603301249s68475c2erdb87c49eec157c0@mail.gmail.com> <20060330205858.GA21147@xor.obsecurity.org> <20060330192437.043e88ff.wmoran@collaborativefusion.com>
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Bill, > > Actually I seem to recall that on Linux with default settings fsync() > > lies and does not actually sync data before returning, so maybe it's > > worth turning off on FreeBSD too if you're comfortable with the > > implications of this. > > If you have fsync off and the system crashes, your PostgreSQL database > will probably be corrupt beyond repair. that is not true. that is not "probable", at least, it never happened to me. and i encountered some panics over the last months ( i have been patching multimedia/pvr250 to support 500s ). in fact, PostgreSQL never corrupted on me in 5 years ( i used to use to mysql, which seemed to corrupt by looking at it ). however, i am not in the large number of transactions-business. there is a sustained number of updates though, at least once every 2 minutes. > I believe the official word from the PostgreSQL folks is that fsync is > safe to turn off if you've got battery-backed cache on your disk > controllers. Many high-end SCSI controllers have this as an option. interesting, i didn't know. > Alternatively, if you're just putting the database on for the first > time, you can temporarily turn fsync off while you're uploading the > data. If the system crashes during this, just delete and recreate > the database and try again. my suggestion to turn fsync of was geared towards this particular problem, although i did not explicitly state that. it is a good thing you are pointing out potential problems. > It's not generally a good idea to run in production with fsync off, > however, unless you have a battery on your controller. While you might be very right, my server only has an UPS, and i am comfortable with that given the stability of FBSD. regards, usleep > > -- > Bill Moran > Potential Technologies > http://www.potentialtech.com >
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