Re: BUG #16031: Group by returns duplicate groups

On Mon, Sep 30, 2019 at 2:49 PM David Raymond <David(dot)Raymond(at)tomtom(dot)com> wrote:
> I re-created the index...
> create index on big_table (name, id_1, id_2);
>
> ...and count(*) goes back to returning 9 again.
>
> and group by sees those 9 as one group and the other 16 as a different group.

You should try running contrib/amcheck, which should be able to confirm
index corruption, and give you a specific complaint. You may then be
able to inspect the exact index page with the problem using
contrib/pageinspect. Something like this ought to do it on Postgres
11:

CREATE EXTENSION IF NOT EXISTS amcheck
SELECT bt_index_check('my_index', true);

If that doesn't show any errors, then perhaps try this:

SELECT bt_index_parent_check('my_index', true);

Let us know what you see.

--
Peter Geoghegan