Oracle error codes


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

This is an Oracle Database Server Message. This can be generated by the Oracle Database when running any Oracle program.

What is the cause of ORA-12520 from Oracle 10g ?

None of the known and available service handlers for requested type of server (dedicated or shared) are appropriate for the client connection.

How to fix ORA-12520 from Oracle 10g ?

Run "lsnrctl services" to ensure that the instance(s) have registered with the listener and that the appropriate handlers are accepting connections.

How to deepen your knowledge about Oracle?

You can train yourself with many books and get an advantage over your competitors by developing a set of skills highly sought throughout the world. Niels Bohr saw an expert as "a person who has found out by his own painful experience all the mistakes that one can make in a very narrow field". So why not you? Be an expert!
To that aim, the first reference book I would suggest is "Oracle Database 11g The Complete Reference (Oracle Press)Oracle Database 11g The Complete Reference" by Kevin Loney. This internationally recognized Oracle expert was named Consultant of the Year by ORACLE Magazine in 2002. Also be aware that the 12c Oracle version is available on here : Oracle Database 12c The Complete Reference (Oracle Press).
In addition to that, let me suggest "OCP Oracle Certified Professional on Oracle 12c Certification Kit" as further reading in order to improve your skills and pass your first level certification.

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Bibliography

Oracle Database 11g The Complete Reference (Oracle Press)Oracle Database 11g The Complete Reference

Oracle Database 11g The Complete ReferenceOracle Database 11g The Complete Reference

The Definitive Guide to Oracle Database 11g.
Get full details on the powerful features of Oracle Database 11g from this thoroughly updated Oracle Press guide. Oracle Database 11g: The Complete Reference explains how to use all the new features and tools, execute powerful SQL queries, construct PL/SQL and SQL*Plus statements, and work with large objects and object-relational databases. Learn how to implement the latest security measures, tune database performance, and deploy grid computing techniques. An invaluable cross-referenced appendix containing Oracle commands, keywords, features, and functions is also included.

Author:

OCP Oracle Certified Professional on Oracle 12c Certification Kit

Meet your certification guide on the journey to Oracle DBA
The Oracle DBA Certification track now consists of three levels – Associate (OCA), Professional (OCP), and Master (OCM). This valuable kit helps you attain success at each level, providing clarification of the complex material along with plenty of practice that covers all exam objectives.
OCP Oracle Certified Professional on Oracle 12c Certification Kit is the ideal tool for preparing for the OCA and OCP exams. With two comprehensive study guides in one package, this kit serves as a helpful companion throughout your journey to Oracle DBA certification. The OCA study guide is designed for those with some Oracle experience and a background in operational management and maintenance, covering one hundred percent of the material on exams 1Z0-061 and 1Z0-062. Once you're OCA certified, the OCP guide prepares you for exam 1Z0-063 by drawing on your experience with backup, recovery, and cloud computing to master database architecture, RMAN, multitenant architecture, and more. Along the way, you'll have access to robust study tools including review questions, bonus practice exam questions, electronic flashcards, and an appendix of additional lab exercises that give you hands-on experience in preparation for exam day.

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Contacting Oracle support services ?

Some messages recommend contacting Oracle Support Services to report a problem. Please go here for more information : Oracle Support.

Linked Oracle error codes

  • ORA-12513 TNS:service handler found but it has registered for a different protocol
  • ORA-12514 TNS:listener does not currently know of service requested in connect descriptor
  • ORA-12515 TNS:listener could not find a handler for this presentation
  • ORA-12516 TNS:listener could not find available handler with matching protocol stack
  • ORA-12518 TNS:listener could not hand off client connection
  • ORA-12519 TNS:no appropriate service handler found
  • ORA-12521 TNS:listener does not currently know of instance requested in connect descriptor
  • ORA-12522 TNS:listener could not find available instance with given INSTANCE_ROLE
  • ORA-12523 TNS:listener could not find instance appropriate for the client connection
  • ORA-12524 TNS:listener could not resolve HANDLER_NAME given in connect descriptor
  • ORA-12525 TNS:listener has not received client's request in time allowed
  • ORA-12526 TNS:listener: all appropriate instances are in restricted mode
  • ORA-12527 TNS:listener: all instances are in restricted mode or blocking new connections
  • ORA-12528 TNS:listener: all appropriate instances are blocking new connections