The values are determined in relation to the system memory on the server.
Make the following changes in postgresql.conf, which is located under PostgreSQL's data directory. A server restart is needed for the change to take effect.
For systems with OVER 4G of memory change the effective_cache_size value calculation from 62.5% to 40% of system memory.
For systems with 4G of memory change the effective_cache_size value calculation from 62.5% to 25% of system memory.
