"Tobias Oberstein" <[EMAIL PROTECTED]> wrote:
> I wonder, this cannot be the case if log entries were written
> fully synchronous. If the Log writer UKT would flush it's log
> queue on every COMMIT, the performance could be at max. :
>
> 7.200 RPM / 60 = 120 records / sec
>
> My harddisk does 7.200 rpms. Best case if the disk head does not
> move at all, but log pages are written out just as the location
> on disk passes the head. This is the case excatly 120 times/sec.
Your understanding of harddisk operation appears to be a leeetle bit
(like, a dozen years) outdated. ;)
Modern disks use a cache that is large compared to the size of a track
and effectively decouple bus transfers and physical disk access.
And more: The calculation above implies that you write one page _per
revolution_, while it is probably safe to assume that you can write
blocks continuously on a track (modulo FS layout policy which is not
relevant for raw devices) almost up to the physical transfer rate of the
disk hardware.
hauke
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