On Tue, Mar 21, 2017 at 10:47 PM, Bruce Momjian <br...@momjian.us> wrote:
> On Tue, Mar 21, 2017 at 01:04:14PM -0400, Robert Haas wrote: > > > I know we have talked about it, but not recently, and if everyone else > > > is fine with it, I am too, but I have to ask these questions. > > > > I think that's a good question. I previously expressed similar > > concerns. On the one hand, it's hard to ignore the fact that, in the > > cases where this wins, it already buys us a lot of performance > > improvement. On the other hand, as you say (and as I said), it eats > > up a lot of bits, and that limits what we can do in the future. On > > the one hand, there is a saying that a bird in the hand is worth two > > in the bush. On the other hand, there is also a saying that one > > should not paint oneself into the corner. > > > > I'm not sure we've had any really substantive discussion of these > > issues. Pavan's response to my previous comments was basically "well, > > I think it's worth it", which is entirely reasonable, because he > > presumably wouldn't have written the patch that way if he thought it > > sucked. But it might not be the only opinion. > > Early in the discussion we talked about allowing multiple changes per > WARM chain if they all changed the same index and were in the same > direction so there were no duplicates, but it was complicated. There > was also discussion about checking the index during INSERT/UPDATE to see > if there was a duplicate. However, those ideas never led to further > discussion. > Well, once I started thinking about how to do vacuum etc, I realised that any mechanism which allows unlimited (even handful) updates per chain is going to be very complex and error prone. But if someone has ideas to do that, I am open. I must say though, it will make an already complex problem even more complex. > > I know the current patch yields good results, but only on a narrow test > case, Hmm. I am kinda surprised you say that because I never thought it was a narrow test case that we are targeting here. But may be I'm wrong. Thanks, Pavan -- Pavan Deolasee http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
