query pegs beta4

This new query of mine pegs beta4, it doesn't return and CPU is at 100%:

    select l.id_location,l.name,
            a.city
            from location l, address a, show_date x, show s, show s2
            where (l.id_address = a.id_address
            and x.id_location = l.id_location
            and s.id_show = x.id_show
            and s2.show_type = s.show_type and s2.id_show = 305)
            or l.id_location = 172;

The tables are not big, at most a few hundred elements each, if that.

Maybe the query itself is flawed, I haven't tried it on other versions
of postgres.