On Wed, Nov 16, 2011 at 11:11 PM, Tom Lane <[email protected]> wrote: > Robert Haas <[email protected]> writes: >> (I wonder if we shouldn't just align every shared memory allocation to >> 64 or 128 bytes. It wouldn't waste much memory and it would make us >> much more resistant to performance changes caused by minor >> modifications to the shared memory layout.) > > I could get behind this idea if we had a reasonably clear idea of the > hardware's cache line width, but AFAIK there is no portable way to > identify that. (This is a pretty fatal objection to Simon's original > patch as well...)
I don't think it's very important to know the exact size. As far as I can tell, x64 is 64 bytes and Itanium and Power are 128 bytes. If you optimize for those, you'll also handle any smaller size (that's a power of two, without which a lot of things we do are wrongheaded) without wasting much memory. If you run into hardware with a giant 256-byte or large cache line, you might have some sharing, but you can't win 'em all. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
