I would suggest to you that something else is wrong. In order for postgresql to use the most efficient method all of the tuning parameters have to be configured properly. The performance list is a better place to discuss this.
How do I tell postgres not to use sequential scan, trough jdbc?
I tried to include 'SET enable_seqscan TO false;' at the begining of the plpgsql function, but that seems to work only if I call the function trough the psql, and only for the subsequent calls in the current session. I 'know' that postgres is using sequential scan because function call takes cca 400ms. When I force postgres not to use sequential scan, the function takes around 5-10ms.
I even tried, on the same connection, to issue 'SET enable_seqscan TO false;' trough jdbc before I call my function, but execution time is still around 400ms.
