1. Identify the root cause of the PostgreSQL 21000 error: The PostgreSQL 21000 error is usually caused by a syntax error in the SQL query. To identify the root cause of the error, you can use the following code snippet to check the syntax of the query:

SELECT * FROM pg_stat_activity WHERE state = 'active';

2. Fix the syntax error:Once you have identified the syntax error, you can fix it by using the following code snippet:

SELECT * FROM pg_stat_activity WHERE state != 'active';

3. Restart the PostgreSQL server:Once the syntax error has been fixed, you can restart the PostgreSQL server to apply the changes. You can use the following code snippet to restart the server:

sudo service postgresql restart

4. Monitor the PostgreSQL server: To ensure that the PostgreSQL server is running smoothly, it is important to monitor it regularly. You can use an automated database observability tool to monitor the server and detect any potential issues.

5. Use an automated database observability tool:An automated database observability tool can help you monitor and fix the PostgreSQL 21000 error. It can detect any potential issues and alert you when they occur. This will help you quickly identify and fix any issues before they become serious.