> select sum(*) from countertable into :cnt;
> delete from countertable;
> insert into countertable (cnt) values (:cnt);
>
> The idea is that you put a script in a scheduler or cron. Depending on
> the average usage of the table, you can set it to run every 1, 5, 15,
> 30, 60 minutes or whatever.

And because the entries in countertable are very short and dense
(minimal fragmentation), even longer interval (say, once a day)
will be sufficient in most cases.

Ivan