PD_ALL_VISIBLE flag was incorrectly set happend during repeatable vacuum

Hi there,

While I trying create reproducible test case for BUG #5798 I
encountered very strange effect on two of my servers (both servers
have same hardware platform/OS (freebsd 7.2) and PostgreSQL 8.4.4).

Very simple test table created as:
CREATE TABLE test (id integer);
INSERT INTO test select generate_series(0,10000);

And I trying repeateble vacuum of that table with script:
perl -e "foreach (1..100000) {system \"psql -d test -h -c 'vacuum test'\";}"

And once per like an minute (really random intervals can be 5 minutes
without problems can be 3 vacuum in row show same error) I getting
next errors:
WARNING: PD_ALL_VISIBLE flag was incorrectly set in relation "test" page 1
...
WARNING: PD_ALL_VISIBLE flag was incorrectly set in relation "test"
page 30 for all pages of the relation.

After that errors script continue vacuums and after some time (0-1000
vacuum loops) I getting the same errors again and so on.
During test run no one touched the test table except my script.

That happened on both of production servers (slony master and slony
slave). However, I can not reproduce this error on other databases
under my support. Complete server restart doesn't make problem
dissapear.

Any ideas what happens there?

--
Maxim Boguk
Senior Postgresql DBA.

Skype: maxim.boguk
Jabber: maxim(dot)boguk(at)gmail(dot)com

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