On Mon, Mar 25, 2013 at 5:57 PM, Greg Stark <st...@mit.edu> wrote: > On Mon, Mar 25, 2013 at 9:53 PM, Kevin Grittner <kgri...@ymail.com> wrote: >> That would make it harder to construct a degenerate case > > I don't think it's hard at all. It's the same as the case Simon wants > to solve except that the cost is incurred in a different way. Imagine > a system where there's a huge data load to a table which is then > read-only for an OLTP system. Until vacuum comes along -- and it may > never since the table never sees deletes or updates -- every > transaction needs to do a clog lookup for every tuple it sees. That > means a significant cpu slowdown for every row lookup forever more. To > save a one-time i/o cost.
That is simply not the case, unless every tuple was created by a unique (or at least non-sequential) transaction xid. There is a 'last transaction id' guard over clog lookup which is pretty effective. The real cost is actually i/o from writing hint bits. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
