FreeBSD MySQL still WAY slower than Linux

[Oliver Fromme]

Michael Schuh <michael.schuh at gmail.com> wrote:
 > 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?

<yoda>
Hope you always can.  But rely on it you should not.
</yoda>
;-)

 >  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.

It's not the dd which decides where to put the file, it's
the filesystem code.  And yes, there can be differences
between RELENG_4 and RELENG_5.  In particular, in RELENG_5
you have UFS2, not the old UFS.  There have always been
changes to the FS code, for example I remember that the
allocation of directories has changed some time ago to
improve metadata performance for large trees (known as
"dirpref").

As I said:  The only way to make sure you hit the same
physical place on the disk is to use a raw partition, not
a file on some filesystem.

Note that even small differences in the placement of the
file can have a noticeable effect on the speed.  Apart
from the speed differences of the disk cylinders, it can
also happen that the file is allocated in a non-contiguous
way, especially if it is large and the filesystem already
contains a lot of files, and/or had a lot of write+delete
operations previously (i.e. causing fragmentation).

 > the part with serial IO related to database-performance have i
 > understand, but i quests me have the others understand
 > my meanings?

That I don't know.

Best regards
   Oliver

-- 
Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München
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