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

[Sean Hinde]

> One thing about mnesia is that it's not really prepared for
> applications that write constantly to disk-based tables.

It is not optimal I agree. There are some relatively simple things which
could be done to improve this though.

One simple idea would be to have independently specified paths to the
various log and dets files. Certainly having the log file on its own disk
could substantially increase performance of the dumper.

Files could also be striped across multiple disks using RAID type systems.

Another more complex enhancement would be to treat the log file as a simple
recovery log and use a memory based store as the actual source for data to
be propogated into the dets files. This could even just contain a list of
keys which have been updated in each transaction and the dumper could get
the data from the main memory table (with some extra stuff for detection of
multiple updates of the same record. Hmmm).

Or there could be a separate UNIX thread which runs through the log and does
the propogation into the main dets files.

I'm sure there are many things which can be done - though splitting out the
path of the different files could perhaps be the simplest and most effective
(allowing one to throw more hardware bandwidth at the problem).

- Sean



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