Pryscila,
> > There are other methods for query optimization, one of them is based on
> > plan transformations (for example, using A-Star algorithm) instead of
> > plan constructions used by PostgreSQL.
We do certainly need a specific optimization for large star-schema joins. I'm
not certain that A* is suitable for our cost model, though; I think we might
need to work up something more particular to Postgres.
> > Does anyone know why this method was choosen? Are there any papers or
> > researches about it?
There probably are on ACM but I've not read them. Ours is a pretty
straightforward implementation of a cost-based optimizer. You can always
read the code ;-)
Mark Kirkwood put together this nice paper on planner statistics:
http://www.powerpostgresql.com/PlanStats
--
Josh Berkus
Aglio Database Solutions
San Francisco