Re: EXPLAIN (ANALYZE, BUFFERS) - puzzling numbers for a simple query.

On Sat, 5 Jun 2021 at 00:55, Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>
> On Sat, 2021-06-05 at 00:12 +1200, David Rowley wrote:
> > As for the call to generate_series, you're not likely to ever get any
> > great estimation from that.  The number of rows returned by a call to
> > that particular function are just whatever is set in pg_proc.prorows,
> > in this case, 1000.  The other generate_series functions which take
> > INT and BIGINT inputs do have a prosupport function.
>
> "generate_series" has a support function from v12 on:

I'd class that as one of "the other generate_series functions", which
I mentioned.  This is not the one being used in this case, which is
why I talked about prorows.

postgres=# select proname,prosupport,prorettype::regtype from pg_proc
where proname = 'generate_series';
     proname     |          prosupport          |         prorettype
-----------------+------------------------------+-----------------------------
 generate_series | generate_series_int4_support | integer
 generate_series | generate_series_int4_support | integer
 generate_series | generate_series_int8_support | bigint
 generate_series | generate_series_int8_support | bigint
 generate_series | -                            | numeric
 generate_series | -                            | numeric
 generate_series | -                            | timestamp without time zone
 generate_series | -                            | timestamp with time zone

I believe the one being used here is the 2nd last one in the above
list.  There's no prosupport function mentioned as of current master.

David