I guessed it was WAL -> actual db files data traffic. It explains why the light stops blinking after shutting down the server (I did it via kill command) .
Do you kill with -15 (the default) or -9? And which process, the postgres master itself or just some random child?
But if so, I expected the light to restart blinking after restarting the server (in order to continue WAL->db activity).
The normal checkpoint is paced. So trickling out data slowly will keep the light on, but not actually stress the system.
When you shutdown the system, it does a fast checkpoint. This gets the data written out as quickly as possible (since you are shutting down, it doesn't worry about interfering with performance for other users, as there are none), so once it is done you don't see the light anymore. If you do a clean shutdown (kill -15 of the postgres master) this fast checkpoint happens upon shutdown. If you do an abort (kill -9) then the fast checkpoint happens upon start-up, once recovery is finished but before the database is opened of regular use.
