On Fri, Jul 13, 2018 at 4:00 AM, Peter Geoghegan <p...@bowt.ie> wrote: > On Tue, Jul 3, 2018 at 5:17 AM, Andrey V. Lepikhov > <a.lepik...@postgrespro.ru> wrote: >> Done. >> Attachment contains an update for use v.2 of the 'Ensure nbtree leaf tuple >> keys are always unique' patch. > > My v3 is still pending, but is now a lot better than v2. There were > bugs in v2 that were fixed. > > One area that might be worth investigating is retail index tuple > deletion performed within the executor in the event of non-HOT > updates. Maybe LP_REDIRECT could be repurposed to mean "ghost record", > at least in unique index tuples with no NULL values. The idea is that > MVCC index scans can skip over those if they've already found a > visible tuple with the same value.
I think that's a good idea. The overhead of marking it as ghost seems small and it would speed up index scans. If MVCC index scans have already found a visible tuples with the same value they can not only skip scanning but also kill them? If can, we can kill index tuples without checking the heap. > Also, when there was about to be a > page split, they could be treated a little bit like LP_DEAD items. Of > course, the ghost bit would have to be treated as a hint that could be > "wrong" (e.g. because the transaction hasn't committed yet), so you'd > have to go to the heap in the context of a page split, to double > check. Also, you'd need heuristics that let you give up on this > strategy when it didn't help. > > I think that this could work well enough for OLTP workloads, and might > be more future-proof than doing it in VACUUM. Though, of course, it's > still very complicated. Agreed. Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
