Remove postmaster.c's check that NBuffers is at least twice MaxBackends.

With the addition of multiple autovacuum workers, our choices were to delete
the check, document the interaction with autovacuum_max_workers, or complicate
the check to try to hide that interaction.  Since this restriction has never
been adequate to ensure backends can't run out of pinnable buffers, it doesn't
really have enough excuse to live to justify the second or third choices.
Per discussion of a complaint from Andreas Kling (see also bug #3888).

This commit also removes several documentation references to this restriction,
but I'm not sure I got them all.

3 files changed, 7 insertions, 24 deletions

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 2c481f93bbf..7a83e075b18 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.552 2008/02/20 22:46:24 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.553 2008/03/09 04:56:28 tgl Exp $
  *
  * NOTES
  *
@@ -688,16 +688,6 @@ PostmasterMain(int argc, char *argv[])
 	/*
 	 * Check for invalid combinations of GUC settings.
 	 */
-	if (NBuffers < 2 * MaxBackends || NBuffers < 16)
-	{
-		/*
-		 * Do not accept -B so small that backends are likely to starve for
-		 * lack of buffers.  The specific choices here are somewhat arbitrary.
-		 */
-		write_stderr("%s: the number of buffers (-B) must be at least twice the number of allowed connections (-N) and at least 16\n", progname);
-		ExitPostmaster(1);
-	}
-
 	if (ReservedBackends >= MaxBackends)
 	{
 		write_stderr("%s: superuser_reserved_connections must be less than max_connections\n", progname);
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 9b33547ed47..1acf2bc0622 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.433 2008/03/06 16:31:42 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.434 2008/03/09 04:56:28 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -1195,16 +1195,10 @@ static struct config_int ConfigureNamesInt[] =
 	},
 
 	/*
-	 * Note: There is some postprocessing done in PostmasterMain() to make
-	 * sure the buffers are at least twice the number of backends, so the
-	 * constraints here are partially unused. Similarly, the superuser
-	 * reserved number is checked to ensure it is less than the max backends
-	 * number.
-	 *
-	 * MaxBackends is limited to INT_MAX/4 because some places compute
-	 * 4*MaxBackends without any overflow check.  This check is made on
+	 * Note: MaxBackends is limited to INT_MAX/4 because some places compute
+	 * 4*MaxBackends without any overflow check.  This check is made in
 	 * assign_maxconnections, since MaxBackends is computed as MaxConnections
-	 * + autovacuum_max_workers.
+	 * plus autovacuum_max_workers.
 	 *
 	 * Likewise we have to limit NBuffers to INT_MAX/2.
 	 */
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 258a7d1a4f5..d3604c2d5c0 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -60,8 +60,7 @@
 #port = 5432				# (change requires restart)
 #max_connections = 100			# (change requires restart)
 # Note:  Increasing max_connections costs ~400 bytes of shared memory per 
-# connection slot, plus lock space (see max_locks_per_transaction).  You might
-# also need to raise shared_buffers to support more connections.
+# connection slot, plus lock space (see max_locks_per_transaction).
 #superuser_reserved_connections = 3	# (change requires restart)
 #unix_socket_directory = ''		# (change requires restart)
 #unix_socket_group = ''			# (change requires restart)
@@ -104,7 +103,7 @@
 
 # - Memory -
 
-#shared_buffers = 32MB			# min 128kB or max_connections*16kB
+#shared_buffers = 32MB			# min 128kB
 					# (change requires restart)
 #temp_buffers = 8MB			# min 800kB
 #max_prepared_transactions = 5		# can be 0 or more