Re: Single-Instance Executable, TSR-style programs, "lockfiles" and the DSA

[Emmanuel Briot <briot.emmanuel@gmail.com>]

> When you moved to DB, did you use the DSA to have a Database-interface partition and client-query/-interface partition? I'm assuming not, because such a ticketing system probably doesn't have enough need for distributed clients, report-generators, etc. to justify such a design.

We did not use the DSA. Postgres itself is a very capable server, which is implemented way more efficiently (and tested way better) than we could ever do I think, since this was only a side job. No reason to add an extra layer between the mail-processing program and the database.

> I suspect such designs are consequences of the poor support for processes/tasking that C has; the Ada equivalent of the functionality would be to have a TASK dedicated to the DB-interfacing [assuming single-node]; for full multi-node DB-backed/-transacted message-exchange DSA makes a lot of sense: Partition your DB-interface into a single node, then have your clients remote-interface that node.

I don't think you need a task dedicated to the database. Postgres handles concurrency very efficiently, it can do asynchronous queries if you really need that, and so on.
If you indeed have a database in your application, you could also use that to handle inter-process locking (pg_advisory_lock() for instance)