Add more documentation about shared memory costs.

diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index f32aa3ff4cb7a28e3c8c3b558b5a9a08633f0be6..6c5ca36e20b87758e14a362ffa26a93e1248ffa3 100644 (file)
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -47,12 +47,15 @@
 #
 #      Shared Memory Size
 #
-#shared_buffers = 64           # min max_connections*2 or 16, 8KB each
-#max_locks_per_transaction = 64        # min 10
-#wal_buffers = 8               # min 4, typically 8KB each
+#shared_buffers = 64           # min 16, at least max_connections*2, 8KB each
+#max_locks_per_transaction = 64        # min 10, ~260*max_connections bytes each
+#wal_buffers = 8               # min 4, 8KB each
 # fsm = free space map
 #max_fsm_relations = 1000      # min 100, ~50 bytes each
 #max_fsm_pages = 20000         # min max_fsm_relations*16, 6 bytes each
+# note: increasing max_connections also costs about 500 bytes each,
+# in addition to costs from shared_buffers and max_locks_per_transaction.
+
 
 #
 #      Non-shared Memory Sizes