On 2017-02-06 16:06:25 -0500, Tom Lane wrote: > Andres Freund <and...@anarazel.de> writes: > > On 2017-02-06 15:39:10 -0500, Peter Eisentraut wrote: > >> On 2/6/17 6:28 AM, Konstantin Knizhnik wrote: > >>> I wonder why do we prohibit now configuration of Postgres without mmap? > > >> It's not really prohibited, but it's not something that people generally > >> need, and we want to keep the number of configuration variations low. > > > I think that was a fairly bad call. Making it hard to use anything but > > mmap (on mmap supporting platforms) caused a fair bit of trouble and > > performance regressions on several platforms by now (freebsd reported it > > fairly quickly, and now aix), all to avoid a trivial amount of code and > > one guc. > > > FWIW, there's a patch somewhere in the archive making it configurable. > > Clearly we should do something, but I'm not sure that a GUC is the right > answer; far too few people would set it correctly. I think it might be > better to have the per-platform "template" files decide whether to set > USE_ANONYMOUS_SHMEM or not.
Well, sysv shmem will be less "comfortable" to use on those platforms too. And you'll usually only hit the performance problems on bigger installations. I don't think it'll be an improvement if after an upgrade postgres doesn't work anymore because people have gotten used to not having to configure sys shmem. I suspect a better solution would be to have a list GUC with a platform dependant default (i.e. sysv, anonymous on freebsd/aix; the other way round on linux). At startup we'd then try those in order. Regards, Andres -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers