What are the reasons for suddenly not being able to con…

Here are some common reasons that may cause connectivity issues with Oracle databases.

1. Issues with the network, such as interruptions in the connection, firewalls blocking database access, and delays in the network, can all potentially result in a failed connection to the Oracle database.
2. The service is not running: The Oracle database service is not started or has been unexpectedly shut down.
3. Invalid SID or service name: an invalid database instance identifier (SID) or service name was used for the connection.
4. Incorrect connection parameters: The connection parameters (such as username, password, host name, port, etc.) are incorrect.
5. License issue: Connection may not be established if Oracle database is expired or the license doesn’t match.
6. The database is full: The storage space of the database has reached its limit or exceeded the preset constraint, making it unable to establish new connections.
7. Database service crash: The database service may crash or experience other malfunctions, resulting in inability to connect.
8. Database instance failure: The database instance may be unable to start due to hardware failure, database file damage, or other reasons.
9. Security restrictions: Database security settings may be limiting some remote connections, resulting in an inability to connect.
10. Authentication issue: Incorrect database username or password, unable to verify identity.

These are just some common reasons, specific reasons need to be investigated based on the specific situation. You can try checking the network connection, confirming if the database service is running properly, and verifying that the connection parameters are correct.