Re: dynamic background workers

On Wed, Jul 3, 2013 at 11:19 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Mon, Jun 24, 2013 at 3:51 AM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
>> 3) Why not adding an other function in worker_spi.c being the opposite
>> of worker_spi_launch to stop dynamic bgworkers for a given index
>> number? This would be only a wrapper of pg_terminate_backend, OK, but
>> at least it would give the user all the information needed to start
>> and to stop a dynamic bgworker with a single extension, here
>> worker_spi.c. It can be painful to stop
>
> Well, there's currently no mechanism for the person who starts a new
> backend to know the PID of the process that actually got started. I
> plan to write a patch to address that problem, but it's not this
> patch.
OK. Understood, this functionality would be a good addition to have.

>> 4) Not completely related to this patch, but one sanity check in
>> SanityCheckBackgroundWorker:bgworker.c is not listed in the
>> documentation: when requesting a database connection, bgworker needs
>> to have access to shmem. It looks that this should be also fixed in
>> REL9_3_STABLE.
>
> That's fine; I think it's separate from this patch. Please feel free
> to propose something.
I'll send a patch about that.

>> 6) Just wondering something: it looks that the current code is not
>> able to identify what was the way used to start a given bgworker.
>> Would it be interesting to be able to identify if a bgworker has been
>> registered though RegisterBackgroundWorker or
>> RegisterDynamicBackgroundWorker?
>
> I don't think that's a good thing to expose.
My concerns here are covered by the functionality you propose in 1),
where a user who launched a custom bgworker would know its PID, this
would allow users to keep track of which bgworker has been started
dynamically.

Regards,
--
Michael