Re: Dynamic background workers & docs question

On Mon, Mar 24, 2014 at 5:54 PM, Magnus Hagander <magnus@hagander.net> wrote:
> I was looking at http://www.postgresql.org/docs/devel/static/bgworker.html
> with a client today.
>
> It says:
> "Unlike RegisterBackgroundWorker, which can only be called from within the
> postmaster,RegisterDynamicBackgroundWorker must be called from a regular
> backend."
>
> Is that the correct restriction? In particular, don't we allow calling
> RegisterDynamicBackgroundWorker from another background worker? (In the
> launcher/worker kind of scenario, like AutoVacuum).

Yes, you can start a dynamic background worker from another background
worker, have a look for example at contrib/worker_spi. Perhaps the
correct wording would be "RegisterDynamicBackgroundWorker must be
called from a regular backend or another background worker".

> Also:
> "Background workers are expected to be continuously running; if they exit
> cleanly, postgres will restart them immediately. "
>
> This doesn't apply to dynamic ones, which we might want to clarify. Do we
> have a "term" for non-dynamic background workers? "static workers"?

In the code or the documentation, there is no explicit
differentiation, bgworkers are either called plainly "bgworker", or
"dynamic bgworker". Perhaps the solution here is simply to say
"background workers started by the postmaster are expected blabla".