Background writer process

This first part of the background writer does no syncing at all.
It's only purpose is to keep the LRU heads clean so that regular
backends seldom to never have to call write().

Jan

src/backend/utils/misc/postgresql.conf.sample

@@ -60,6 +60,11 @@
 #vacuum_mem = 8192		# min 1024, size in KB
 #debug_shared_buffers = 0	# 0-600 seconds
 
+# - Background writer -
+#bgwriter_delay = 200		# 10-5000 milliseconds
+#bgwriter_percent = 1		# 0-100% of dirty buffers
+#bgwriter_maxpages = 100	# 1-1000 buffers max at once
+
 # - Free Space Map -
 
 #max_fsm_pages = 20000		# min max_fsm_relations*16, 6 bytes each