On Sat, Jul 21, 2018 at 3:11 AM, Peter Geoghegan <p...@bowt.ie> wrote: > On Thu, Jul 19, 2018 at 4:29 AM, Masahiko Sawada <sawada.m...@gmail.com> > wrote: >>> 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. > > I think you're talking about making LP_REDIRECT marking in nbtree > represent a "recently dead" hint: the deleting transaction has > committed, and so we are 100% sure that the tuple is about to become > garbage, but it cannot be LP_DEAD just yet because it needs to stay > around for the benefit of at least one existing snapshot/long running > transaction. > > That's a different idea to what I talked about, since it could perhaps > work in a way that's much closer to LP_DEAD/kill_prior_tuple (no extra > executor stuff is required).
I understood. Thank you for explanation! Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
