Issue #1947: postgresql: set synchronous_commit to off

Author: valyala

config/postgresql.conf

@@ -166,7 +166,7 @@ random_page_cost = 2
 #wal_level = minimal			# minimal, archive, or hot_standby
 					# (change requires restart)
 #fsync = on				# turns forced synchronization on or off
-#synchronous_commit = on		# synchronization level; on, off, or local
+synchronous_commit = off		# synchronization level; on, off, or local
 #wal_sync_method = fsync		# the default is the first option
 					# supported by the operating system:
 					#   open_datasync