Gregory Stark wrote: > > "Heikki Linnakangas" <[EMAIL PROTECTED]> writes: > > > There is one wacky idea I haven't dared to propose yet: > > > > We could lift the limitation that you can't defragment a page that's > > pinned, if we play some smoke and mirrors in the buffer manager. When > > you prune a page, make a *copy* of the page you're pruning, and keep > > both versions in the buffer cache. Old pointers keep pointing to the old > > version. Any new calls to ReadBuffer will return the new copy, and the > > old copy can be dropped when its pin count drops to zero. > > Fwiw when Heikki first mentioned this idea I thought it was the craziest thing > I ever heard. But the more I thought about it the more I liked it. I've come > to the conclusion that while it's a wart, it's not much worse than the wart of > the super-exclusive lock which it replaces. In fact it's arguably cleaner in > some ways.
I read this as very similar to RCU. In some scenarios it makes a lot of sense. I don't think it's a thing to be attacked in 8.3 though, since it is a big change to the bufmgr. -- Alvaro Herrera http://www.advogato.org/person/alvherre "The Postgresql hackers have what I call a "NASA space shot" mentality. Quite refreshing in a world of "weekend drag racer" developers." (Scott Marlowe) ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
