Nodes and fastNodes are stored under the database with different key formats to ensure there are no key collisions and a structured key from which we can extract useful information.
Node KeyFormat: n|node.nodeKey.version|node.nodeKey.nonce
Nodes are marshalled and stored under nodekey with prefix n to prevent collisions and then appended with the node's hash.
FastNode KeyFormat: f|node.key
FastNodes are marshalled nodes stored with prefix f to prevent collisions. You can extract fast nodes from the database by iterating over the keys with prefix f.