I have created a database link but I get this error when I try to use the link: "ORA-02068: following a severe error from RTX510 ORA-01034:oracle not available ORA-07429." However the other database is available and running.
The database link requires a TNS alias, which you specified in the USING clause of the CREATE DATABASE LINK command. Outside of Oracle, check to ensure that you can use this TNS alias to connect to the database. Using SQL*Plus, see if you can connect to this remote database:
My guess is that the above will give you the same error. This means that either the TNS alias is defined incorrectly, or the instance is not really running. If you can connect with SQL*Plus, the database link should work just fine.