On Sat, Sep 24, 2011 at 9:45 AM, Martijn van Oosterhout <klep...@svana.org> wrote: > I think memory accesses are also fantastically expensive, so it's worth > some effort to optimise that.
This is definitely true. > I found the Linux kernel document on this topic quite readable. I think > the main lesson here is that processors track data dependancies (other > than the Alpha apparently), but not control dependancies. So in the > example, the value of i is dependant on num_items, but not via any > calculation. IThat control dependancies are not tracked makes some > sense, since branches depend on flags bit, and just about any > calculation changes the flag bits, but most of the time these changes > are not used. Oh, that's interesting. So that implies that a read-barrier would be needed here even on non-Alpha. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers