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

Shawn Pearce <>
Tue Jan 2 22:54:31 CET 2001


Andi Kleen <> scrawled:
> On Tue, Jan 02, 2001 at 03:49:16PM -0500, Shawn Pearce wrote:
> > Oracle does this with their database and it is a big performance
> > booster.  The other thing they do is allow a table to be striped
> > across multiple disks by making a table exist in multiple file system
> > files at once.  (They stripe disk allocations across the files.)  This
> > does help to manage larger tables as well.
> 
> Near all modern OS can do that themselves using volume managers and software
> RAID -- it would probably be a waste of time to implement it in Mnesia too.

This is true, and I agree.  However, it does allow Oracle to easily
handle >2GB datafiles on Unixes that cannot deal with it.  It also
lets you stick to 32 bit file offsets by adding a file number
``prefix''.

Keep in mind its nice to be able to split backups onto tapes by
designing the database datafiles such that one data file fits onto a
tape.  Or a cluster of datafiles fits onto a tape.  What if we have a
100GB database, how do we dump it onto 20GB tapes??  If its one huge
file, its harder to dump than if its a collection of 10GB files.  Or
1GB files that can be put on tape at 20 (or 19) files at a time.

But striping may be out of the question.  Maybe its just a linear
joining?

Anyway, just a thought on top of my other comments with Mnesia.

--
Shawn.

  ``If this had been a real
    life, you would have
    received instructions
    on where to go and what
    to do.''



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