title: Amazon RDS (PostgreSQL): Optimize memory usage
body: <p>There is something i did not really understand with Amazon RDS (the PostrgreSQL version). Some queries takes a lot of time to show their results. I have set all relevant indexes (as shown with EXPLAIN). So I think it's not due to my schema design.</p>
  
  <p>I do not use a big machine (m3.xlarge) as bigger ones are too much expensive. My database size is about 300GB.</p>
  
  <p>It seems that Postgres does not use all the available memory (only ~5GB, the "Freeable memory" report of the console shows that there are always ~10GB freeable...). I try to tune my "parameter group" as proposed by <a href="http://www.davidmkerr.com/2013/11/tune-your-postgres-rds-instance-via.html" rel="noreferrer">tune-your-postgres-rds-instance</a>, especially set EFFECTIVE_CACHE_SIZE to 70%. But it does not change anything.</p>
  
  <p>I'm probably wrong somewhere... Any idea ?</p>