Listener (lsnrctl) reload vs stop/start Some blogs tell that reload is equal stop and start, but in my test it does not stop the listener (uptime does not change).

What situation can I use only reload and when I must stop/start the listener? Is stop/start for just validate the applied configuration for all current connections? (force the all connections to reconnect in listener)?
reloading your listener will allow listener to take new changes (configuration) without stopping it, and it will un-register\register dynamically registered DBs.

stop will stop listener completely by disallowing new session to connect to the database remotely.

start will start listener and this will allow users to continue working on the database.

for me I usually use listener reload for production to make sure I dont have any downtime during working hours. stop\start incase we need to perform some maintenance