FreeBSD MySQL still WAY slower than Linux
michael.schuh at gmail.com
Tue Jun 21 15:01:52 GMT 2005
ahhhhh, that are the hint that i missed.
now i have another question, if i use the same Os in 2 versions
(RELENG_4, RELENG_5) can i hope that the tests are made on the same
part of disk?
or in other words can an dd on the two OS' es so much different
because they use an
totally other part of disk? I think no, the strategie from dd under
one OS should not be changed if the OS-Version has changed.
the part with serial IO related to database-performance have i
understand, but i quests me have the others understand
2005/6/21, Oliver Fromme <olli at lurza.secnetix.de>:
> Michael Schuh <michael.schuh at gmail.com> wrote:
> > As i sayed i have the installations always made in the same way, so that i mean.
> > I mean i have alwas made the swap on the first gig of the disk, and
> > the installation
> > on the rest of the disk. and i have no multiple os'es on these disk.
> The problem is that the file (from "dd of=foo") can still
> end up at completely different physical places on the disk.
> It depends on the filesystem (ext2, ext3, UFS, whatever)
> and on the allocation strategies of the filesystem code.
> UFS might start filling cylinder groups from the beginning
> of the disk, while ext3 might start at the end (does ext3
> even _have_ cylinder groups?). This was just an example,
> but you get the idea.
> Of course, it also depends on how much data there already
> is on the filesystem, and how it is distributed over the
> For accurate measurements and comparisons, you have to make
> sure to use _exactly_ the same physical location on the
> disk. From userland you don't have a way to control the
> physical allocation of files. Therefore, the only reliable
> way is to leave an unused partition on the disk, do _not_
> put a filesystem on it, and use the raw device in the »dd«
> command. If you do this, you will always hit the same
> physical location on the disk.
> But then again -- as others have already mentioned, serial
> write speed is not the most important factor for database
> performance (although the WAL journal files of advanced
> transactional databases like PostgreSQL are written in a
> sequential way), so the usefulness of this "benchmark" is
> very debatable.
> Best regards
> Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München
> Any opinions expressed in this message may be personal to the author
> and may not necessarily reflect the opinions of secnetix in any way.
> "I started using PostgreSQL around a month ago, and the feeling is
> similar to the switch from Linux to FreeBSD in '96 -- 'wow!'."
> -- Oddbjorn Steffensen
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