Steve Wampler <swampler(at)noao(dot)edu> writes:
> So, leave COUNT(*) alone. But it would be very handy to have a
> way to get an approximate table size that is more accurate than is
> provided by a pg_class.reltuples that is only updated on vacuums.
If you want something cheap, you could use the same technique the
planner uses nowadays: take RelationGetNumberOfBlocks() (which is
guaranteed accurate) and multiply by reltuples/relpages. I don't
see anyplace where RelationGetNumberOfBlocks is directly exposed to
users now, but it'd be trivial to code up a couple of C functions to
provide this functionality.
regards, tom lane