Horton

make MaxBackends available in _PG_init

Wang, Shenhao <wangsh.fnst@cn.fujitsu.com>

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From: "Wang, Shenhao" <wangsh.fnst@cn.fujitsu.com>
To: "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2020-09-21T03:43:41Z
Lists: pgsql-hackers

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Hi Hackers:

I find the value in function _PG_init, the value of MaxBackends is 0.
In source, I find that the postmaster will first load library, and then calculate the value of MaxBackends.

In the old version, the MaxBackends was calculated by:
	 MaxBackends = MaxConnections + autovacuum_max_workers + 1 +
		GetNumShmemAttachedBgworkers();
Because any extension can register workers which will affect the return value of GetNumShmemAttachedBgworkers.
InitializeMaxBackends must be called after shared_preload_libraries. This is also mentioned in comments.

Now, function GetNumShmemAttachedBgworkers was deleted and replaced by guc max_worker_processes, 
so if we changed the calling order like:
	Step1: calling InitializeMaxBackends.
	Step2: calling process_shared_preload_libraries

In this order extension can get the correct value of MaxBackends in _PG_init.

Any thoughts?

Regards

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