On Mon, 21 Nov 2022 at 15:01, Tom Lane <t...@sss.pgh.pa.us> wrote: > > > What we need is a solution that avoids reading an unbounded number of > > tuples under any circumstances. I previously suggested using > > SnapshotAny here, but Tom didn't like that. I'm not sure if there are > > safety issues there or if Tom was just concerned about the results > > being misleading. Either way, maybe there's some variant on that theme > > that could work. For instance, could we teach the index scan to stop > > if the first 100 tuples that it finds are all invisible? Or to reach > > at most 1 page, or at most 10 pages, or something? > > A hard limit on the number of index pages examined seems like it > might be a good idea.
Good, that is what the patch does. > > If we don't find a > > match, we could either try to use a dead tuple, or we could just > > return false which, I think, would end up using the value from > > pg_statistic rather than any updated value. > > Yeah, the latter seems like the best bet. Yes, just breaking out of the loop is enough to use the default value. > If we do install such a thing, should we undo any of the previous > changes that backed off the reliability of the result? Not sure. -- Simon Riggs http://www.EnterpriseDB.com/
