Re: BitmapHeapScan streaming read user and prelim refactoring

On Sun, Apr 7, 2024 at 10:42 PM Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
wrote:

> create table t (a int, b int) with (fillfactor=10);
> insert into t select mod((i/22),2), (i/22) from generate_series(0,1000)
> S(i);
> create index on t(a);
> vacuum analyze t;
>
> set enable_indexonlyscan = off;
> set enable_seqscan = off;
> explain (analyze, verbose) select 1 from (values (1)) s(x) where exists
> (select * from t where a = x);
>
> KABOOM!

FWIW, it seems to me that this assert could be triggered in cases where,
during a join, not all inner tuples need to be scanned before skipping to
next outer tuple. This can happen for 'single_match' or anti-join.

The query provided by Tomas is an example of 'single_match' case. Here
is a query for anti-join that can also trigger this assert.

explain (analyze, verbose)
select t1.a from t t1 left join t t2 on t2.a = 1 where t2.a is null;
server closed the connection unexpectedly

Thanks
Richard