while reading more about postgresql I came across a discussion which is valid for oracle, too: it’s about implementing hints in the postgresql optimizer. actually it is more about why the postgresql people do not want to provide a feature like this.
for developing and testing purposes there might be situations where hints are useful. but hints do not solve the issue, hints are always a workaround. I like the way the postgresql people think about this: fix the problem ( either in the application or the postgresql source code ).
check out the pros, cons and discussions:
postgresql optimizer hint discussion
Hinting at PostgreSQL
Daniel Westermann's Blog 