Re: Misaligned BufferDescriptors causing major performance problems on AMD

On Thu, Feb  6, 2014 at 09:40:32AM +0100, Andres Freund wrote:
> On 2014-02-05 12:36:42 -0500, Robert Haas wrote:
> > >> It may well be that your proposal is spot on.  But I'd like to see some
> > >> data-structure-by-data-structure measurements, rather than assuming that
> > >> alignment must be a good thing.
> > >
> > > I am fine with just aligning BufferDescriptors properly. That has
> > > clearly shown massive improvements.
> > 
> > I thought your previous idea of increasing BUFFERALIGN to 64 bytes had
> > a lot to recommend it.
> 
> Good.
> 
> I wonder if we shouldn't move that bit of logic:
> 	if (size >= BUFSIZ)
> 		newStart = BUFFERALIGN(newStart);
> out of ShmemAlloc() and instead have a ShmemAllocAligned() and
> ShmemInitStructAligned() that does it. So we can sensibly can control it
> per struct.
> 
> > But that doesn't mean it doesn't need testing.
> 
> I feel the need here, to say that I never said it doesn't need testing
> and never thought it didn't...

Where are we on this?

--  Bruce Momjian          http://momjian.us EnterpriseDB                             http://enterprisedb.com
 + Everyone has their own god. +