Re: Inconsistency in startup process's MyBackendId and procsignal array registration with ProcSignalInit()

On Wed, Oct 13, 2021 at 4:25 AM Andres Freund <andres@anarazel.de> wrote:
>
> Hi,
>
> On 2021-10-11 15:24:46 +0900, Fujii Masao wrote:
> > How about modifying SharedInvalBackendInit() so that it accepts
> > BackendId as an argument and allocates the ProcState entry of
> > the specified BackendId? That is, the startup process determines
> > that its BackendId is "MaxBackends + MyAuxProcType (=StartupProcess) + 1"
> > in AuxiliaryProcessMain(), and then it passes that BackendId to
> > SharedInvalBackendInit() in InitRecoveryTransactionEnvironment().
>
> If I understand correctly what you're proposing, I think that's going in the
> wrong direction. We should work towards getting rid of BackendIds
> instead. This whole complication vanishes if we make sinvaladt use pgprocno.
>
> See https://postgr.es/m/20210802171255.k4yv5cfqaqbuuy6f%40alap3.anarazel.de
> for some discussion of this.

Will any of the backends get pgprocno greater than MaxBackends? The
pgprocno can range from 0 to ((MaxBackends + NUM_AUXILIARY_PROCS +
max_prepared_xacts) - 1) and the ProcState array size is MaxBackends.
How do we put a backend with pgprocno > MaxBackends, into the
ProcState array? Is it that we also increase ProcState array size to
(MaxBackends + NUM_AUXILIARY_PROCS + max_prepared_xacts)? Probably
this is the dumbest thing as some slots are unused
(NUM_AUXILIARY_PROCS - 1 + max_prepared_xacts slots. -1 because the
startup process needs a ProcState slot) and the shared memory is
wasted.

Regards,
Bharath Rupireddy.