> 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.
Create 2 sequences, one for counting tuple additions and one for
counting tuple deletions.
When you INSERT a tuple, bump the "added" sequence (select nextval());
When you DELETE a tuple, bump the "deleted" sequence (select nextval());
To retrieve an approximate count, take the current value of both
sequences (select directly -- don't use currval) and subtract the
"deletes" from the "adds".
This is a very fast tracking mechanism with the catch that it does not
handle rollbacks -- but you only wanted approximate. Put all of the
logic inside a pair of triggers and a function within the DB.
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