Re: Very strange postgresql behaviour

Arnau <arnaulist(at)andromeiberica(dot)com> writes:
> I have postgresql 7.4.2 running on debian and I have the oddest
> postgresql behaviour I've ever seen.

Is this specific to these two rows? If so it might be a case of this
bug, which was repaired in 7.4.13:

http://archives.postgresql.org/pgsql-general/2006-05/msg00756.php
http://archives.postgresql.org/pgsql-committers/2006-05/msg00174.php

2006-05-19 12:31 tgl

* src/backend/executor/nodeIndexscan.c (REL7_4_STABLE): Fix nasty
bug in nodeIndexscan.c's detection of duplicate tuples during a
multiple (OR'ed) indexscan. It was checking for duplicate
tuple->t_data->t_ctid, when what it should be checking is
tuple->t_self. The trouble situation occurs when a live tuple has
t_ctid not pointing to itself, which can happen if an attempted
UPDATE was rolled back. After a VACUUM, an unrelated tuple could
be installed where the failed update tuple was, leading to one live
tuple's t_ctid pointing to an unrelated tuple. If one of these
tuples is fetched by an earlier OR'ed indexscan and the other by a
later indexscan, nodeIndexscan.c would incorrectly ignore the
second tuple. The bug exists in all 7.4.* and 8.0.* versions, but
not in earlier or later branches because this code was only used in
those releases. Per trouble report from Rafael Martinez Guerrero.

REINDEX wouldn't fix this, although a table dump and reload would.

regards, tom lane

PS: please don't spam multiple lists with the same question.