On Thu, Aug 31, 2023 at 2:32 PM David Christensen <david.christen...@crunchydata.com> wrote: > Here's a patch atop the series which converts to 16-bit uints and > passes regressions, but I don't consider well-vetted at this point.
For what it's worth, my gut reaction to this patch series is similar to that of Andres: I think it will be a disaster. If the disaster is not evident to us, that's far more likely to mean that we've failed to test the right things than it is to mean that there is no disaster. I don't see that there is a lot of upside, either. I don't think we have a lot of evidence that changing the block size is really going to help performance. In fact, my guess is that there are large amounts of code that are heavily optimized, without the authors even realizing it, for 8kB blocks, because that's what we've always had. If we had much larger or smaller blocks, the structure of heap pages or of the various index AMs used for blocks might no longer be optimal, or might be less optimal than they are for an 8kB block size. If you use really large blocks, your blocks may need more internal structure than we have today in order to avoid CPU inefficiencies. I suspect there's been so little testing of non-default block sizes that I wouldn't even count on the code to not be outright buggy. If we could find a safe way to get rid of full page writes, I would certainly agree that that was worth considering. I'm not sure that anything in this thread adds up to that being a reasonable way to go, but the savings would be massive. I feel like the proposal here is a bit like deciding to change the speed limit on all American highways from 65 mph or whatever it is to 130 mph or 32.5 mph and see which way works out best. The whole infrastructure has basically been designed around the current rules. The rate of curvature of the roads is appropriate for the speed that you're currently allowed to drive on them. The vehicles are optimized for long-term operation at about that speed. The people who drive the vehicles are accustomed to driving at that speed, and the people who maintain them are accustomed to the problems that happen when you drive them at that speed. Just changing the speed limit doesn't change all that other stuff, and changing all that other stuff is a truly massive undertaking. Maybe this example somewhat overstates the difficulties here, but I do think the difficulties are considerable. The fact that we have 8kB block sizes has affected the thinking of hundreds of developers over decades in making thousands or tens of thousands or hundreds of thousands of decisions about algorithm selection and page format and all kinds of stuff. Even if some other page size seems to work better in a certain context, it's pretty hard to believe that it has much chance of being better overall, even without the added overhead of run-time configuration. -- Robert Haas EDB: http://www.enterprisedb.com
