On Mon, Jul 24, 2017 at 2:43 PM, Peter Geoghegan <p...@bowt.ie> wrote: > On Mon, Jul 24, 2017 at 10:13 AM, Claudio Freire <klaussfre...@gmail.com> > wrote: >> Vacuum *might* be able to redistribute tuples too, while holding locks >> to all 3 pages (the two children and the parent page), since it can >> move the TID to the middle point of two actual child TIDs, mindlessly, >> without checking to see if such TID actually exists - it just needs to >> choose a TID cutoff point that will distribute item pointers evently. >> I haven't tried this, but it is theoretically possible. > > I don't understand what you mean here. As long as the TIDs are a first > class part of the keyspace, what VACUUM does or doesn't do should not > matter. Page deletion stashes a TID in the highkey position of a leaf > page within _bt_mark_page_halfdead(), but that shouldn't matter to > you. > > I guess you're talking about contriving a TID value that is the mean > of two real TID values -- the two that are on each side of the split > point during a leaf page split. While that seems possible, I don't see > much value in it. Unless you have normalized keys, you can only really > truncate whole attributes. And, I think it's a bad idea to truncate > anything other than the new high key for leaf pages, with or without > normalized keys. Changing the keys once they're in internal pages is > never going to be worth it.
That's what I'm saying. It might not be worth it. I haven't tested yet. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
