On 2015-01-28 10:58:40 -0500, Tom Lane wrote: > Andres Freund <and...@2ndquadrant.com> writes: > > On 2015-01-28 10:35:28 -0500, Tom Lane wrote: > >> Even if you didn't have plans like that, it would be entire folly to > >> imagine that buffer headers will be exactly 64 bytes without some forcing > >> function for that. > > > Meh. The 128 byte additionally used by the alignment don't hurt in any > > case. But forcing all buffer descriptors to 64bit on a 32bit platform > > isn't guaranteed to be performance neutral. > > > So, no I don't think it's a "folly" to do so. > > Once we have the mechanism in place, it is a policy decision whether to > apply it on 32-bit builds. If you don't think there is evidence to > support aligning headers on 32-bit builds, we don't have to do that.
I just have no idea whether it'd be beneficial to use more space on 32bit to pad the individual entries. Since this mostly is beneficial on multi-socket, highly concurrent workloads, I doubt it really matter. > But I firmly object to applying a patch that claims to align the headers > on 64-bit platforms unless it includes something to ensure that it > *actually* does that, regardless of platform variations or subsequent > additions or subtractions of fields. Well, the patch claims to align the buffer descriptor *array* not the individual descriptors... I personally still think that a comment above sbufdesc's definition would be sufficient for now. But whatever. I'll enforce 64byte padding on 64bit platforms, and do nothing on 32bit platforms. > I think that's a necessary component > of any such patch and should not be allowed to slide. If you don't want > to do that work now, then drop the topic until you do. Man. This style of comment really is just sad. -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
