On Wed, Mar 30, 2011 at 10:43 AM, Alvaro Herrera <alvhe...@commandprompt.com> wrote: > Excerpts from Merlin Moncure's message of mié mar 30 12:14:20 -0300 2011: > >> It is very different -- the slru layer is in shared memory and >> requires locks to access. The entire point is trying to avoid >> accessing this structure in tight code paths. I'm actually very >> skeptical the slru layer provides any benefit at all. I bet it would >> be cheaper just mmap in the pages directly (as Heikki is also >> speculating). > > Maybe it would be useful to distinguish the last SLRU page(s) (the one > where clog writing actually takes place) from the older ones (which only > ever see reading). You definitely need locks to be able to access the > active pages, but all the rest could be held as mmapped and accessed > without locks because they never change (except to be truncated away). > You know that any page behind RecentXmin is not going to be written > anymore, so why go through all the locking hoops?
hm, that's a good thought -- cheap and easy -- and good to implement irrespective of other changes. any improvement helps here, although from my perspective the largest hobgoblins are shared memory access generally and the extra i/o. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
