Mnesia disk performance (was RE: multi-attribute mnesia indexes?)

[Andi Kleen]

On Wed, Jan 03, 2001 at 10:08:25AM +0100, Ulf Wiger wrote:
> I must confess that I haven't kept up with OS vs DBMS design in the
> past few years, but it used to be commonly accepted that you simply
> couldn't build a really fast DBMS on top of the standard file and
> memory management provided by the leading operating systems --
> certainly not if you wanted similar behaviour across multiple
> platforms. I don't know if it's still true...

The file systems have catched up a lot and often databases are run in
files these days now. On a modern extent based fs with preallocated files
you basically do raw IO in the extents.

If you want 100% the same behaviour everywhere you'll of course need to 
do it from scratch, but it'll cost you in effort, and increases the 
mainteance effort required by administrators a lot. 


> 
> One DBMS I worked with was Cincom's SUPRA. I remember that you had the
> choice upon installing the database whether you wanted it to reside on
> a normal file system (good for testing) or on a raw partition (good
> for speed). In the case of the raw partition, SUPRA would use its own
> file I/O driver.

Not really an option anymore (using own drivers), except for some very
special cases. 


-Andi