Consequently, this patch is a separate process launched by postmaster, that periodically write()'s out "some" dirty buffers in LRU order. This causes the buffers returned for replacement (when a backend needs to read in a page) to be clean allways. The process does no sync(), fsync() or any other calls thus far. Nothing has changed in the checkpoint logic either.
The configuration options controlling the process are all PGC_SIGHUP:
# - 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
Delay is the number of milliseconds to wait between loops. If there was nothing to do at all in one loop (all buffers clean), then the process will sleep for 10 seconds.
Percent is the percentage of "dirty pages" to write per loop. This is independant of the size of the buffer pool. If percent = 0 the postmaster will not start the process at all.
Maxpages is an upper bound to prevent the background writer from producing a write storm if a sequential operation causes all pages of a large buffer pool to be dirtied at once.
Jan
-- #======================================================================# # It's easier to get forgiveness for being wrong than for being right. # # Let's break this rule - forgive me. # #================================================== [EMAIL PROTECTED] #
---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
