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RAC: Connections to SCAN Listeners Consistently Fail with an ORA-12520 or ORA-12516 Error (Doc ID 2111134.1)

Last updated on MARCH 31, 2022

Applies to:

Oracle Net Services - Version and later
Oracle Database - Enterprise Edition - Version and later
Information in this document applies to any platform.
This document refers specifically to cases where the ORA-12520 or ORA-12516 error occurs consistently. The LSNRCTL services output might show the instance handler in state:blocked.
An intermittent ORA-12520/12516 would not be due to the kind of misconfiguration issue that is documented here.


Each connection to SCAN listener fails with the ORA-12520 error.  A level 16 listener
trace reveals this stack when all 3 SCAN addresses are tried:

ORA-12520: TNS:listener could not find available handler for requested type of server

The SCAN listener log files show the TNS-12516 error also:

TNS-12516 TNS: listener could not find instance with matching protocol stack

A check of the VIP listener logs reveals no errors.  More importantly, there is no indication
of any connections being logged by VIP listeners.

The handler appears in READY state at the SCAN listener when issuing LSNRCTL services or status.

This is a persistent and not an intermittent error. 


 This is likely a new implementation of RAC or the LOCAL_LISTENER and/or REMOTE_LISTENER settings have been changed.


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