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
You would use RELOAD in a busy system where you can't afford denied connections. Reload is typically used when you make a change to listener.ora and you want the changes to activate immediately for all new connections. Sometimes the change might contain a bug (and you can't really test it unless you reload), and then this extends the time taken to revert your changes, assuming you made a backup of listener.ora. Good luck if you don't have a backup, as finding the bug (like a missing bracket) can be time consuming.
We use STOP/START when DBSNMP misbehaves. Stopping the listener usually disconnects all DBSNMP sessions but sometimes we have to kill DBSNMP from within the database. DBSNMP misbehaves in times of bad performance and has a backlog of stats to receive from the agent. This creates a vicious cycle and makes performance worse.
In the rare event that we have to CLEARSTATE, then we STOP first, CLEARSTATE and then START.
use reload if changing some parameter in the existing configuration. for example using "set" command to change valid_node_checking_registration.
use restart if you have made some significant changes like added another port for the same listener. using normal reload wont have any effect
