Re: archive modules

On 11/2/21, 9:46 AM, "Robert Haas" <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Nov 2, 2021 at 12:39 PM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:>
>> On 11/2/21, 9:17 AM, "Robert Haas" <robertmhaas(at)gmail(dot)com> wrote:
>> You could still introduce GUCs in _PG_init(), but they couldn't be
>> defined as PGC_POSTMASTER.
>
> It seems like PGC_POSTMASTER isn't very desirable anyway. Wouldn't you
> want PGC_SIGHUP? I mean I'm not saying there couldn't be a case where
> that wouldn't work, because you could need a big chunk of shared
> memory allocated at startup time or something. But in that's probably
> not typical, and if it does happen well then that particular archive
> module has to be preloaded. If you know that you have several archive
> modules that you want to use, you can still preload them all if for
> this or any other reason you want to do that. But in a lot of cases
> it's not going to be necessary.
>
> In other words, if we use hooks, then you're guaranteed to need a
> server restart to change anything. If we use something like what you
> have now, there can be corner cases where you need that or benefits of
> preloading, but it's not a hard requirement, and in many cases you can
> get by without it. That seems strictly better to me ... but maybe I'm
> still confused.
>
>> Also, you could still use
>> RegisterDynamicBackgroundWorker() to register a background worker, but
>> you couldn't use RegisterBackgroundWorker(). These might be
>> acceptable restrictions if swapping archive libraries on the fly seems
>> more important, but I wanted to bring that front and center to make
>> sure everyone understands the tradeoffs.
>
> RegisterDynamicBackgroundWorker() seems way better, though. It's hard
> for me to understand why this would be a problem for anybody. And
> again, if somebody does have that need, they can always fall back to
> saying that their particular module should be preloaded if you want to
> use it.

I agree. I'll make sure the archive library can be changed via SIGHUP
in the next revision.

Nathan