Re: recovery modules

Hi,

On 2023-02-13 14:56:47 -0800, Nathan Bossart wrote:
> On Mon, Feb 13, 2023 at 04:37:10PM +0900, Michael Paquier wrote:
> > + basic_archive_context = data->context;
> > + if (CurrentMemoryContext == basic_archive_context)
> > + MemoryContextSwitchTo(TopMemoryContext);
> > +
> > + if (MemoryContextIsValid(basic_archive_context))
> > + MemoryContextDelete(basic_archive_context);
> >
> > This is a bit confusing, because it means that we enter in the
> > shutdown callback with one context, but exit it under
> > TopMemoryContext. Are you sure that this will be OK when there could
> > be multiple callbacks piled up with before_shmem_exit()? shmem_exit()
> > has nothing specific to memory contexts.
>
> Well, we can't free the memory context while we are in it, so we have to
> switch to another one. I agree that this is a bit confusing, though.

Why would we be in that memory context? I'd just add an assert documenting
we're not.

> On second thought, I'm not sure it's important to make sure the state is
> freed in the shutdown callback. It's only called just before the archiver
> process exits, so we're not really at risk of leaking anything. I suppose
> we might not always restart the archiver in this case, but I also don't
> anticipate that behavior changing in the near future. I think this
> callback is more useful for things like shutting down background workers.

I think it's crucial. Otherwise we're just ossifying the design that there's
just one archive module active at a time.

> I went ahead and removed the shutdown callback from basic_archive and the
> note about leaking from the documentation.

-1

Greetings,

Andres Freund