I am a newbie, as you all know, but I am still embarassed asking this question. I started my tuning career by changing shared_buffers. Soon I discovered that I was hitting up against the available RAM on the system. So, I brought the number down. Then I discovered max_fsm_pages. I could take that up quite high and found out that it is a 'disk' thing. Then I started increasing checkpoint_segments,which is also a disk thing. However, setting it to 25, and then increasing any of the other 2 variables, the postgresql daemon stops working. meaning it does not start upon reboot. When I bring shared_buffers or max_fsm_pages back down, the daemon starts and all is normal. This happens on a 1 GB RAM machine and a 4 GB RAM machine.