threads - use them as much as you can

[Sean Hinde]

> > In R7B (the current release) there is a new feature which 
> introduces a pool
> > of native threads for i/o operations but this is disabled 
> by default. This
> > will get around the hanging problem /.../ 

I thought some more about my original reply and should probably add that
during testing I have absolutely hammered mnesia with database writes to a
disc_copies table at full speed, while at the same time having another node
performing timed reads at 100 per second on the same table (all on a single
processor 167 MHz SPARC :o) ).

The worst blocking I got under standard Unix File System was a pause of 5
seconds which only occurred occasionally during the mnesia log dump. The
vast majority of reads were returned in millisecs.

Using Veritas File system (or I guess any of the other new journaling file
systems) I never managed to get the disk writing node to block my reads for
more than 1.5 seconds under these conditions (again 1 in thousands).

My conclusion was that the Erlang VM does a pretty incredible job of
managing this real time stuff - far far better than quite a number of
commercial databases I have come across.

Note that this was without multithreaded i/o... And It's getting better,
better all the time.

- Sean



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