Robert(dot)Farrugia(at)go(dot)com(dot)mt writes:
> Running a slightly modified query i.e. removing the in and using an
> equality, the planner uses the "correct" index this time.
Hm. What were the definitions of the two indexes, exactly?
There is an asymmetry in the planner's handling of AND/OR clauses that
can cause it to fail to recognize that a multicolumn index is usable,
depending on whether the OR clause (the IN part of your query) applies
to the first index column or a later one. I'm not sure if this relates
to your problem or not, though...
regards, tom lane