On Wed, Jul 8, 2015 at 1:27 PM, Andres Freund <and...@anarazel.de> wrote:
> On 2015-07-08 13:46:53 -0500, Merlin Moncure wrote: > > On Wed, Jul 8, 2015 at 12:48 PM, Craig James <cja...@emolecules.com> > wrote: > > > On Tue, Jul 7, 2015 at 10:31 PM, Joshua D. Drake <j...@commandprompt.com > > > > >> Using Apache Fast-CGI, you are going to fork a process for each > instance > > >> of the function being executed and that in turn will use all CPUs up > to the > > >> max available resource. > > >> > > >> With PostgreSQL, that isn't going to happen unless you are running (at > > >> least) 8 functions across 8 connections. > > > > > > > > > Well, right, which is why I mentioned "even with dozens of clients." > > > Shouldn't that scale to at least all of the CPUs in use if the > function is > > > CPU intensive (which it is)? > > > > only in the absence of inter-process locking and cache line bouncing. > > And addititionally memory bandwidth (shared between everything, even in > the numa case), cross socket/bus bandwidth (absolutely performance > critical in multi-socket configurations), cache capacity (shared between > cores, and sometimes even sockets!). > >From my admittedly naive point of view, it's hard to see why any of this matters. I have functions that do purely CPU-intensive mathematical calculations ... you could imagine something like is_prime(N) that determines if N is a prime number. I have eight clients that connect to eight backends. Each client issues an SQL command like, "select is_prime(N)" where N is a simple number. Are you saying that in order to calculate is_prime(N), all of that stuff (inter-process locking, memory bandwith, bus bandwidth, cache capacity, etc.) is even relevant? And if so, how is it that Postgres is so different from an Apache fast-CGI program that runs the exact same is_prime(N) calculation? Just curious ... as I said, I've already implemented a different solution. Craig
