Centuries ago, Nostradamus foresaw when [EMAIL PROTECTED] (Tom Lane) would write: > I thought we had sufficiently destroyed that "reuse a tuple" meme > yesterday. You can't do that: there are too many aspects of the system > design that are predicated on the assumption that dead tuples do not > come back to life.
This discussion needs to come up again in October when the zombie movies come out :-). > That's the other problem: it's not apparent why pushing work from > vacuum back into foreground processing is a good idea. Especially > not why retail vacuuming of individual tuples will be better than > wholesale. What is unclear to me in the discussion is whether or not this is invalidating the item on the TODO list... ------------------- Create a bitmap of pages that need vacuuming Instead of sequentially scanning the entire table, have the background writer or some other process record pages that have expired rows, then VACUUM can look at just those pages rather than the entire table. In the event of a system crash, the bitmap would probably be invalidated. One complexity is that index entries still have to be vacuumed, and doing this without an index scan (by using the heap values to find the index entry) might be slow and unreliable, especially for user-defined index functions. ------------------- It strikes me as a non-starter to draw vacuum work directly into the foreground; there is a *clear* loss in that the death of the tuple can't actually take place at that point, due to MVCC and the fact that it is likely that other transactions will be present, keeping the tuple from being destroyed. But it would *seem* attractive to do what is in the TODO, above. Alas, the user defined index functions make cleanout of indexes much more troublesome :-(. But what's in the TODO is still "wholesale," albeit involving more targetted selling than the usual Kirby VACUUM :-). -- select 'cbbrowne' || '@' || 'gmail.com'; http://linuxdatabases.info/info/rdbms.html Rules of the Evil Overlord #140. "I will instruct my guards when checking a cell that appears empty to look for the chamber pot. If the chamber pot is still there, then the prisoner has escaped and they may enter and search for clues. If the chamber pot is not there, then either the prisoner is perched above the lintel waiting to strike them with it or else he decided to take it as a souvenir (in which case he is obviously deeply disturbed and poses no threat). Either way, there's no point in entering." <http://www.eviloverlord.com/> ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
