On Fri, Aug 19, 2011 at 9:19 AM, Gokulakannan Somasundaram <gokul...@gmail.com> wrote: > The fact that the > proposal is for crash safe visibility map, to become a default package of > any Postgresql table will definitely have wide ranging implications on OLTP > performance.
Well, that would certainly be alarming if true, but I don't think it is. As far as I can see, the overhead of making the visibility map crash-safe is just (1) a very small percentage increase in the work being done by VACUUM and (2) a slight possibility of extra work done by a foreground process if the visibility map bit changes at almost exactly the same time the process was about to insert, update, or delete a tuple. If someone comes up with a test where this overhead is enough to measure, then we might need to rethink our whole approach. Maybe we would make it an optional feature, or maybe we would just rip it out and start over with some sort of redesign, or maybe we would look for other optimizations to counterbalance the additional overhead. I don't know. But as far as I can see you're hypothesizing without evidence. -- 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