Date: Fri, 17 Aug 2018 11:04:11 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andrew Gierth <andrew@tao11.riddles.org.uk>
Cc: pgsql-bugs@lists.postgresql.org, v.g.baranoff@gmail.com
Subject: Re: BUG #15336: Wrong cursor's bacward fetch results in select with
 ALL(subquery)
Message-ID: <20180817140411.crhfn3machmctt7n@alvherre.pgsql>
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On 2018-Aug-17, Andrew Gierth wrote:

> I wonder if we have a contender here for the oldest reported bug in PG
> history; while I haven't tested anything older than 9.5, the incorrect
> logic seems to date back to the introduction of subqueries in
> 6.something.

Hmm ..

> begin;
> declare foo cursor for select * from generate_series(1,3) i where i <> all (values (2));
> fetch all from foo;  -- returns the expected 2 rows
> fetch backward all from foo;  -- assertion failure, or incorrect result

8.2 seems fine:

alvherre=# show debug_assertions;
 debug_assertions 
------------------
 on
(1 fila)

alvherre=# begin;
BEGIN
alvherre=# declare foo cursor for select * from generate_series(1,3) i where i <> all (values (2));
DECLARE CURSOR
alvherre=# fetch all from foo;
 i 
---
 1
 3
(2 filas)
alvherre=# fetch backward all from foo;
 i 
---
 3
 1
(2 filas)

9.1 does fail an assertion:

TRAP: FailedAssertion(Ť!(forward || (readptr->eflags & 0x0004))ť, Archivo: Ť/pgsql/source/REL9_1_STABLE/src/backend/utils/sort/tuplestore.cť, Línea: 765)

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services