Database link and event “single-task message”

Today I had a problem with a private database link between two databases. The user reports that running a simple “desc dual@pluto.cartoons.com” doesn’t work.  Currently in the source database are three sessions hung. If we look at that do these sessions, we can see that are waiting for the event single-task message.

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This event usually occurs across the database link connection. We tried to perform a tnsping to check the listener.

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Tnsping command doesn’t reply, so we can determine that the problem is the listener, try perform a lsnrctl status but not responding so we opted to finish the process with the command “kill -9” since we are on unix platform and restart the listener. In the source database the first three sessiones continue unanswered so we kill, in this case from database.

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The kill command reply “ORA-00031: session marked for kill”. The sessions continue but do not die, so we kill them using kill command from Operating System .

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