RE: Some shared memory chunks are allocated even if related processes won't start

Dear Tom,

Thanks for replying!

> "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com> writes:
> > While reading codes, I found that ApplyLauncherShmemInit() and
> AutoVacuumShmemInit()
> > are always called even if they would not be launched.
> > It may be able to reduce the start time to avoid the unnecessary allocation.
>
> Why would this be a good idea?  It would require preventing the
> decision not to launch them from being changed later, except via
> postmaster restart.

Right. It is important to relax their GucContext.

> We've generally been trying to move away
> from unchangeable-without-restart decisions.  In your example,
>
> > +    if (max_logical_replication_workers == 0 || IsBinaryUpgrade)
> > +        return;
>
> max_logical_replication_workers is already PGC_POSTMASTER so there's
> not any immediate loss of flexibility, but I don't think it's a great
> idea to introduce another reason why it has to be PGC_POSTMASTER.

You are right. The first example implied the max_logical_replication_workers
won't be changed. So it is not appropriate.
So ... what about second one? The approach allows to allocate a memory after
startup, which means that users may able to change the parameter from 0 to
natural number in future. (Of course, such an operation is prohibit for now).
Can it be an initial step to ease the condition?

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/