Horton

Re: make MaxBackends available in _PG_init

Nathan Bossart <bossartn@amazon.com>

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From: "Bossart, Nathan" <bossartn@amazon.com>
To: Greg Sabino Mullane <htamfids@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2021-08-10T00:22:50Z
Lists: pgsql-hackers

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On 8/9/21, 1:14 PM, "Greg Sabino Mullane" <htamfids@gmail.com> wrote:
> Giving this a review.

Thanks for your review.

> However, the more I went through this patch, the more the GetMaxBackends(0) nagged at me. The vast majority of the calls are with "0". I'd argue for just having no arguments at all, which removes a bit of code and actually makes things like this easier to read:

I agree.  The argument is nonzero in less than half of the calls to
GetMaxBackends(), and I'm not sure it adds a whole lot of value in the
first place.  I removed the argument in v3.

>> + * This must be called after modules have had the change to alter GUCs in
>> + * shared_preload_libraries, and before shared memory size is determined.
> s/change/chance/;

I fixed this in v3.

>> +void
>> +SetMaxBackends(int max_backends)
>> +{
>> + if (MaxBackendsInitialized)
>> +  elog(ERROR, "MaxBackends already initialized");
>
> Is this going to get tripped by a call from restore_backend_variables?

I ran 'make check-world' with EXEC_BACKEND with no problems, so I
don't think so.

Nathan

Commits

  1. Add a new shmem_request_hook hook.

  2. Remove non-functional code for unloading loadable modules.

  3. Fix misleading comments about background worker registration.

  4. Revert the addition of GetMaxBackends() and related stuff.

  5. Fix typo in multixact.c

  6. Reduce more the number of calls to GetMaxBackends()

  7. Remove MaxBackends variable in favor of GetMaxBackends() function.

  8. Fix comments about bgworker registration before MaxBackends initialization

  9. Fix bogus assertion in BootstrapModeMain().

  10. Make sure MaxBackends is always set