Checkpoint is not getting completing properly. There is delay of more than 3 hrs between checkpoints. Manual intiated checkpoint running for more than 1 hour.
Checkpoint_timeout 5min
Max wal size 8gb
OK, your checkpoints take a long time to complete and since they don't run concurrently having a checkpoint_timeout value less than that time to complete renders the setting immaterial. The main question here is what factors into how long a checkpoint takes to complete. IIUC there are two pieces, the amount of shared buffers being written to disk and the rate at which they are written. So the main driver of this whole setup is "shared_buffers".