On Wed, 2024-10-02 at 21:55 +1300, David Rowley wrote:
> On Tue, 1 Oct 2024 at 06:17, Laurenz Albe <laurenz.albe@cybertec.at> wrote:
> > Why did you change "Disabled" from an integer to a boolean?
>
> I just don't think "Disabled Nodes" is all that self-documenting and
> I'm also unsure why the full integer value of disabled_nodes is
> required over just displaying the boolean value of if the node is
> disabled or not. Won't readers look at the remainder of the plan to
> determine information about which other nodes are disabled? Do we need
> to give them a running total?
I didn't want a running total, but maybe I misunderstood what a disabled
node is; see below.
> > If you see a join where two plans were disabled, that's useful information.
>
> I'm not sure if I follow what you mean here. The patch will show
> "Disabled: true" for both the inner and outer side of the join if both
> of those are disabled. The difference is that my patch does not show
> the join itself is disabled like master does. I thought that's what
> you were complaining about. Can you show an example of what you mean?
I ran the following example, and now I am confused.
CREATE TABLE tab_a (id integer);
CREATE TABLE tab_b (id integer);
SET enable_nestloop = off;
SET enable_hashjoin = off;
EXPLAIN SELECT * FROM tab_a JOIN tab_b USING (id);
QUERY PLAN
═════════════════════════════════════════════════════════════════════
Merge Join (cost=359.57..860.00 rows=32512 width=4)
Merge Cond: (tab_a.id = tab_b.id)
-> Sort (cost=179.78..186.16 rows=2550 width=4)
Sort Key: tab_a.id
-> Seq Scan on tab_a (cost=0.00..35.50 rows=2550 width=4)
-> Sort (cost=179.78..186.16 rows=2550 width=4)
Sort Key: tab_b.id
-> Seq Scan on tab_b (cost=0.00..35.50 rows=2550 width=4)
I would have expected to see "Disabled nodes: 2" with the merge join,
because both the nested loop join and the hash join have been disabled.
Why is there no disabled node shown?
Yours,
Laurenz Albe
