Re: Server crashed with dense_rank on partition table.

On 2018-06-13 16:35:58 +0900, Amit Langote wrote:
> Hi.
>
> On 2018/06/13 14:55, Michael Paquier wrote:
> > On Wed, Jun 13, 2018 at 11:08:38AM +0530, Rajkumar Raghuwanshi wrote:
> >> postgres=# SELECT dense_rank(b) WITHIN GROUP (ORDER BY a) FROM pagg_tab
> >> GROUP BY b ORDER BY 1;
> >> server closed the connection unexpectedly
> >> This probably means the server terminated abnormally
> >> before or while processing the request.
> >> The connection to the server was lost. Attempting reset: Failed.
> >
> > Indeed, thanks for the test case. This used to work in v10 but this is
> > failing with v11 so I am adding an open item. The plans of the pre-10
> > query and the query on HEAD are rather similar, and the memory context
> > at execution time looks messed up.
>
> Fwiw, I see that the crash can also occur even when using a
> non-partitioned table in the query, as shown in the following example
> which reuses Rajkumar's test data and query:
>
> create table foo (a int, b int, c text);
> postgres=# insert into foo select i%20, i%30, to_char(i%12, 'FM0000') from
> generate_series(0, 36) i;
>
> select dense_rank(b) within group (order by a) from foo group by b order by 1;
> server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
> The connection to the server was lost. Attempting reset: Failed.
>
> Following query in the regression test suite can also be made to crash by
> adding a group by clause:
>
> select dense_rank(3) within group (order by x) from (values
> (1),(1),(2),(2),(3),(3),(4)) v(x) group by (x);
> server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
> The connection to the server was lost. Attempting reset: Failed.
>
> Looking at the core dump of this, it seems the following commit may be
> relevant:
>
> commit bf6c614a2f2c58312b3be34a47e7fb7362e07bcb
> Author: Andres Freund <andres(at)anarazel(dot)de>
> Date: Thu Feb 15 21:55:31 2018 -0800
>
> Do execGrouping.c via expression eval machinery, take two.

Andres, with RMT hat on: Andres, this needs looking at ASAP.
Andres, without RMT hat on: Oh, I had first missed it, and then was
distracted reviewing pluggable storage.
Andres, with RMT hat on: that's not really an excuse
Andres, without RMT hat on: sorry, will start looking now.

Greetings,

Andres Freund