On 2013-04-22 11:27:25 -0400, Robert Haas wrote: > On Wed, Apr 17, 2013 at 8:21 PM, Greg Smith <g...@2ndquadrant.com> wrote: > >> The more I read of this thread, the more unhappy I get. It appears that > >> the entire design process is being driven by micro-optimization for CPUs > >> being built by Intel in 2013. > > > > And that's not going to get anyone past review, since all the tests I've > > been doing the last two weeks are on how fast an AMD Opteron 6234 with OS > > cache >> shared_buffers can run this. The main thing I'm still worried > > about is what happens when you have a fast machine that can move memory > > around very quickly and an in-memory workload, but it's hamstrung by the > > checksum computation--and it's not a 2013 Intel machine. > > This is a good point. However, I don't completely agree with the > conclusion that we shouldn't be worrying about any of this right now. > While I agree with Tom that it's far too late to think about any > CPU-specific optimizations for 9.3, I have a lot of concern, based on > Ants's numbers, that we've picked a checksum algorithm which is hard > to optimize for performance. If we don't get that fixed for 9.3, > we're potentially looking at inflicting many years of serious > suffering on our user base. If we at least get the *algorithm* right > now, we can worry about optimizing it later. If we get it wrong, > we'll be living with the consequence of that for a really long time. > > I wish that we had not scheduled beta quite so soon, as I am sure > there will be even more resistance to changing this after beta. But > I'm having a hard time escaping the conclusion that we're on the edge > of shipping something we will later regret quite deeply. Maybe I'm > wrong?
I don't see us changing away from CRCs anymore either by now. But I think at least changing the polynom to something that a) has higher error detection properties b) can noticeably sped up on a a good part of the hardware pg is run on If we are feeling really adventurous we can switch to a faster CRC implementation, there are enough ones around and I know that at least my proposed patch from some years ago (which is by far not the fastest that is doable) is in production usage some places. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers