Re: elegant and effective way for running jobs inside a database

On Tue, Mar 6, 2012 at 12:47 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> And also some interface.  It'd be useful to have background jobs that
> executed either immediately or at a certain time or after a certain
> delay, as well as repeating jobs that execute at a certain interval or
> on a certain schedule.  Figuring out what all that should look like
> is, well, part of the work that someone has to do.

Certainly.  It would seem to make sense to have a database schema
indicating this kind of metadata.

It needs to be sophisticated enough to cover *enough* unusual cases.

A schema duplicating crontab might look something like:
create table cron ( id serial primary key, minutes integer[], hours text integer[], dayofmonth integer[], month
integer[],dayofweek integer[], command text 
);

That's probably a bit too minimalist, and that only properly supports
one user's crontab.

The schema needs to include things like:
a) When to perform actions.  Several bases for this, including
time-based, event-based.
b) What actions to perform (including context as to database user,
search_path, desired UNIX $PWD, perhaps more than that)
c) Sequencing information, including what jobs should NOT be run concurrently.
d) Logging.  If a job succeeds, that should be noted.  If it fails,
that should be noted.  Want to know start + end times.
e) What to do on failure.  "Everything blows up" is not a good answer :-).
--
When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"