Re: BUG #18260: Unexpected error: "negative bitmapset member not allowed" triggered by multiple JOIN

On 28/12/2023 10:03, Richard Guo wrote:
> During that time, join removal was only performed for left joins, so it
> was not possible for 'ojrelid' to be negative.  However, with the
> introduction of the SJE feature, inner joins can also be removed, and
> 'ojrelid' is set to -1 in the inner join case.  That's how we see this
> error.
Agreed, I have come to the same conclusion.

>         if (bms_is_subset(phinfo->ph_needed, joinrelids) &&
>             bms_is_member(relid, phinfo->ph_eval_at) &&
> -           !bms_is_member(ojrelid, phinfo->ph_eval_at))
> +           (sjinfo == NULL || !bms_is_member(ojrelid, phinfo->ph_eval_at)))
It would be better to check "ojrelid >= 0" as a sign. But why do you
think SJE could need to delete PlaceHolderVar at all?
>
> Alternatively, we can modify bms_is_member() to return false for
> negative numbers instead of emitting an error, as suggested by the
> comment there.
> -   /* XXX better to just return false for x<0 ? */
> +   /* negative number cannot be a member of the bitmapset */
>     if (x < 0)
> -       elog(ERROR, "negative bitmapset member not allowed");
> +       return false;
>
> I prefer the second option, but I'm open to other thoughts.
I don't like this option. It could mask some blunders somewhere like a
current one.

> FWIW, here is a simplified repro for this error.
>
> create table t (a int primary key, b int);
>
> explain (verbose, costs off)
> select 1 from t t1 left join
>     (lateral (select 1 as x, * from t t2) s1 inner join
>         (select * from t t3) s2 on s1.a = s2.a)
>     on true
> where s1.x = 1;
> ERROR:  negative bitmapset member not allowed
It can be simplified even more (without LATERAL):
explain (verbose, costs off)
select 1 from t t1 left join
(select 1 as x, * from t t2) s1 inner join
(select * from t t3) using (a)
on true
where s1.x = 1;

--
regards,
Andrei Lepikhov
Postgres Professional