BUG #7858: Inaccurate Log Message

On Fri, Feb 8, 2013 at 06:46:29AM +0000, jackie.qq.zhang@gmail.com wrote:

The following bug has been logged on the website:

Bug reference: 7858
Logged by: Jackie Zhang
Email address: jackie.qq.zhang@gmail.com
PostgreSQL version: 9.1.4
Operating system: Ubuntu
Description:

Hi,

The log message of the sanity check for "superuser_reserved_connections" in
PostmasterMain() is not accurate. See the following code snippet:

/*src/backend/postmaster/postmaster.c*/
730 /*
731 * Check for invalid combinations of GUC settings.
732 */
733 if (ReservedBackends >= MaxBackends)
734 {
735 write_stderr("%s: superuser_reserved_connections must
be less than max_connections\n", progname);
736 ExitPostmaster(1);
737 }

The problem is that "MaxBackends" is calculated by both
"autovacuum_max_workers" and "max_connections". See assign_maxconnections()
and assign_autovacuum_max_workers() in src/backend/utils/misc/guc.c.

The log message should inform both the two configuration parameters instead
of only one -- the root cause could be the oversized
"autovacuum_max_workers".

The calculation, ReservedBackends >= MaxBackends, was corrected in
Postgres 9.3 with this commit:

commit b3055ab4fb5839a872bfe354b2b5ac31e6903ed6
Author: Magnus Hagander <magnus@hagander.net>
Date: Fri Aug 10 14:49:03 2012 +0200

Fix upper limit of superuser_reserved_connections, add limit for wal_senders

Should be limited to the maximum number of connections excluding
autovacuum workers, not including.

Add similar check for max_wal_senders, which should never be higher than
max_connections.

--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +

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