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Add new GUC reserved_connections.

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This provides a way to reserve connection slots for non-superusers.
The slots reserved via the new GUC are available only to users who
have the new predefined role pg_use_reserved_connections.
superuser_reserved_connections remains as a final reserve in case
reserved_connections has been exhausted.

Patch by Nathan Bossart. Reviewed by Tushar Ahuja and by me.

Discussion: http://postgr.es/m/20230119194601.GA4105788@nathanxps13
This commit is contained in:
Robert Haas
2023-01-20 15:36:36 -05:00
parent fe00fec1f5
commit 6e2775e4d4
10 changed files with 115 additions and 25 deletions
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29
src/backend/postmaster/postmaster.c
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@@ -205,14 +205,24 @@ char *ListenAddresses;
/*
* SuperuserReservedConnections is the number of backends reserved for
* superuser use. This number is taken out of the pool size given by
* MaxConnections so number of backend slots available to non-superusers is
* (MaxConnections - SuperuserReservedConnections). Note what this really
* means is "if there are <= SuperuserReservedConnections connections
* available, only superusers can make new connections" --- pre-existing
* superuser connections don't count against the limit.
* superuser use, and ReservedConnections is the number of backends reserved
* for use by roles with privileges of the pg_use_reserved_connections
* predefined role. These are taken out of the pool of MaxConnections backend
* slots, so the number of backend slots available for roles that are neither
* superuser nor have privileges of pg_use_reserved_connections is
* (MaxConnections - SuperuserReservedConnections - ReservedConnections).
*
* If the number of remaining slots is less than or equal to
* SuperuserReservedConnections, only superusers can make new connections. If
* the number of remaining slots is greater than SuperuserReservedConnections
* but less than or equal to
* (SuperuserReservedConnections + ReservedConnections), only superusers and
* roles with privileges of pg_use_reserved_connections can make new
* connections. Note that pre-existing superuser and
* pg_use_reserved_connections connections don't count against the limits.
*/
int SuperuserReservedConnections;
int ReservedConnections;
/* The socket(s) we're listening to. */
#define MAXLISTEN 64
@@ -908,11 +918,12 @@ PostmasterMain(int argc, char *argv[])
/*
* Check for invalid combinations of GUC settings.
*/
if (SuperuserReservedConnections >= MaxConnections)
if (SuperuserReservedConnections + ReservedConnections >= MaxConnections)
{
write_stderr("%s: superuser_reserved_connections (%d) must be less than max_connections (%d)\n",
write_stderr("%s: superuser_reserved_connections (%d) plus reserved_connections (%d) must be less than max_connections (%d)\n",
progname,
SuperuserReservedConnections, MaxConnections);
SuperuserReservedConnections, ReservedConnections,
MaxConnections);
ExitPostmaster(1);
}
if (XLogArchiveMode > ARCHIVE_MODE_OFF && wal_level == WAL_LEVEL_MINIMAL)