After a failover of an instance, a connection to an instance might become read-only, and then issue 25006 SQL errors on a PostgreSQL instance. 

This has been described in https://github.com/keycloak/keycloak/issues/24493. 

While I think the better option is to have validation query, as it would prevent an error from happening in the first place, I wonder if checking for SQL Code in 25006 in PostgreSQLExceptionSorter could be added as well to clean up after the fact. 

I briefly had the idea of asking the connection if is marked with isReadOnly(), but I found that the connection is inaccessible in the ExceptionSorter.