On Fri, Jan 27, 2012 at 10:05 PM, Jeff Janes <jeff.ja...@gmail.com> wrote: > On Sat, Jan 21, 2012 at 7:31 AM, Simon Riggs <si...@2ndquadrant.com> wrote: >> >> Yes, it was. Sorry about that. New version attached, retesting while >> you read this. > > In my hands I could never get this patch to do anything. The new > cache was never used. > > I think that that was because RecentXminPageno never budged from -1. > > I think that that, in turn, is because the comparison below can never > return true, because the comparison is casting both sides to uint, and > -1 cast to uint is very large > > /* When we commit advance ClogCtl's shared RecentXminPageno if needed > */ > if (ClogCtl->shared->RecentXminPageno < > TransactionIdToPage(RecentXmin)) > ClogCtl->shared->RecentXminPageno = > TransactionIdToPage(RecentXmin);
Thanks, will look again. > Also, I think the general approach is wrong. The only reason to have > these pages in shared memory is that we can control access to them to > prevent write/write and read/write corruption. Since these pages are > never written, they don't need to be in shared memory. Just read > each page into backend-local memory as it is needed, either > palloc/pfree each time or using a single reserved block for the > lifetime of the session. Let the kernel worry about caching them so > that the above mentioned reads are cheap. Will think on that. -- Simon Riggs 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
