On 03/25/2012 09:00 PM, Bill House wrote:
> Regarding the statistics, I have since learned that the command:
>
> select reltuples from pg_class where relname = 'your_file_name';
>
> Will give a record count. I don't know how well it will keep up in a
> dynamic environment but it's a start.
reltuples "is only an estimate used by the planner." See
http://www.postgresql.org/docs/9.1/static/catalog-pg-class.html
So if you want a more or less accurate count of rows at that given point
in time, then you should not depend on it.
As for the optimization of SELECT count(*) which Adrian had mentioned,
it's a 9.2 feature (as a result of index-only scans). See
https://wiki.postgresql.org/wiki/Todo under Cache Usage.
Joe