They work as expected for English. They "work" for languages with characters outside the English set, but they order based on ASCII byte values rather than the order expected by native speakers. Proper collation is a TODO for r17.

I made these changes to postgresql.conf and restarted postgresql:

random_page_cost = 1.0

effective_cache_size = 11GB

shared_buffers = 3GB

The times for load, index and the queries were about the same as for the published run.

My apologies, I should have said earlier & in the blog that PostgreSQL is _CPU bound_ even before I made these changes. Next time I will also track CPU and disk usage and publish those for more clarity.

I've re-run EXPLAIN and done a bit more digging than before, looks like PostgreSQL does not use the "username" index to do the GROUP BY, I suspect it's related to this: http://archives.postgresql.org/pgsql-bugs/2008-02/msg00220.p...

Thanks again!