Workflow management system in Erlang/Mnesia?
Tue Jan 25 10:10:54 CET 2000
> I came across Mnesia and Erlang these days and got the impression that it
> may be a cool environment to implement an open source, web-based,
> distributed, fault-tolerant workflow management system that we intend to
> use as the basis for a laboratory management system. I'm writing this
> message in the hope to get feedback on whether Erlang/Mnesia is a good
> choice for this and whether my expectations are realistic.
You can find an example of an Open Source Erlang/Mnesia/Web
> * does Erlang/Mnesia sound like a good solution for this problem in
> * does Erlang automatically offer load-balancing distribution of processing
> similar to pvm?
> If not, can this be added and with how much effort ?
I guess this is very application dependent. However, there already
exist a library call 'pool', from the man-page:
pool can be used to run a set of Erlang nodes as a pool of
computational processors. It is organized as a master and
a set of slave nodes and includes the following features:
* The slave nodes send regular reports to the master
about their current load.
* Queries can be sent to the master to determine which
node will have the least load.
The BIF statistics(run_queue) is used for estimating
future loads. It returns the length of the queue of ready
to run processes in the Erlang system.
When it comes to the question about fault-tolerance it can be
as simple as using the HEART facility to automatically restart
an Erlang node, or as 'complicated' as the Bluetail Mail Robustifier
(http://www.bluetail.com). For example I had good use of the
former mechanism in the Ticket system mentioned above. I had a bug
which sometimes caused the whole system to crash, but since it was
restarted automatically the (Web) clients just noticed a long
delay which was fixed by hitting the reload button (at that
time the sytem was back in operation again with no data lost).
Torbjörn Törnkvist , tel: +46 8 692 22 15 , fax: +46 8 654 70 71
Bluetail AB , Hantverkargatan 78 , SE-112 38 Stockholm , Sweden
Email: , Web: http://www.bluetail.com/~tobbe
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