Re: Misaligned BufferDescriptors causing major performance problems on AMD

Andres Freund <andres(at)2ndquadrant(dot)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.
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. 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.

regards, tom lane