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

On Mon, Oct 11, 2021 at 11:54 AM Fujii Masao
<masao(dot)fujii(at)oss(dot)nttdata(dot)com> 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 we do the above, then the problem might arise if somebody calls
SICleanupQueue and wants to signal the startup process, the below code
(from SICleanupQueue) can't get the startup process backend id. So,
the backend id calculation for the startup process can't just be
MaxBackends + MyAuxProcType + 1.
BackendId his_backendId = (needSig - &segP->procState[0]) + 1;

> Maybe you need to enlarge ProcState array so that it also handles
> auxiliary processes if it does not for now.

It looks like we need to increase the size of the ProcState array by 1
at least (for the startup process). Currently the ProcState array
doesn't have entries for auxiliary processes, it does have entries for
MaxBackends. The startup process is eating up one slot from
MaxBackends. Since we need only an extra ProcState array slot for the
startup process I think we could just extend its size by 1. Instead of
modifying the MaxBackends definition, we can just add 1 (and a comment
saying this 1 is for startup process) to shmInvalBuffer->maxBackends
in SInvalShmemSize, CreateSharedInvalidationState. IMO, this has to go
in a separate patch and probably in a separate thread. Thoughts?

Regards,
Bharath Rupireddy.