Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> I'm thinking of removing cmin and cmax, and keeping that information in
> backend-private memory instead.
I don't believe you can remove *both*. What's been discussed is
removing one of them, by letting the field represent a lookup key for an
in-memory structure in the infrequent case that xmin and xmax are both
the current xact. You solve the table size problem by only having one
entry for each unique cmin/cmax pair in use.
regards, tom lane