Before we decided in our installation to head toward recursive queries, we were fiddling as well with the page costs. We could persuade in some queries pg to use the index, in some queries we had to turn off the optimizer, and we had to rearrange queries, etc. Improving the results from some queries often worsen the results on others, some queries were still not effected, the results were not really encouraging; furthermore, for packaging openacs in distros, recommended configuration changes make life more complicated.
From our experience getting rid of the huge materialized tree tables (having many duplicate keys), and move towards recursive queries looks much more promising. As effect, e.g. permission queries are now several times faster with 9.0 then they were with 8.3 (we are using the recursive queries in production since summer). However, this path requires some data model changes. Victor has the packaging of the changes in a more or less non-destructive way mostly done, just a matter of days. The package will be made available to the brave (i.e. early adapters). Depending on the results we can decide via TIP, whether that should go into the main branches.
