From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
---|---|
To: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
Cc: | Pól Ua Laoínecháin <linehanp(at)tcd(dot)ie>, PostgreSQL General <pgsql-general(at)lists(dot)postgresql(dot)org> |
Subject: | Re: EXPLAIN (ANALYZE, BUFFERS) - puzzling numbers for a simple query. |
Date: | 2021-06-04 13:40:36 |
Message-ID: | CAApHDvp=0R=ELsgsE8FSw2ZzoiG9rb00YWCYU6kPeHaeum-hvg@mail.gmail.com |
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Lists: | pgsql-general |
On Sat, 5 Jun 2021 at 00:55, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)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
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