Many Oracle DBAs, developers and just end-users often encounter an issue when they can not connect remotely to an Oracle database. There can be different reasons of the connection problems. I give below a short cookbook on resolving those database connection issues. But first let’s explore a bit Oracle connectivity concepts and terminology.
An Oracle database is represented to clients as a service; that is, the database performs work on behalf of clients. The service name is included in the connect data part of the connect descriptor. To connect to a database service, clients use a connect descriptor that provides the location of the database and the name of the database service. The address portion of the connect descriptor is actually the protocol address of the listener. To connect to a database service, clients first contact a listener process that typically resides on the database server. The listener receives incoming client connection requests and hands these requests to the database server. Once the connection is established, the client and database server communicate directly. Read more »
Issue / Oracle error
SQL*Plus: Release 10.2.0.5.0 - Production on Wed May 18 09:32:35 2011
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ORA-12547: TNS :lost contact when try to connect to Oracle.
I saw that TNS connection issue along with ORA-12547 Oracle error several times, usually when trying to connect to Oracle database server on Unix / Linux host with an OS user that does not belong to oinstall group (Oracle binaries owner group). In this case, interesting enough that local TNS connection to database (when using tnsnames alias) works fine: Read more »
Oracle database 11gR2 (220.127.116.11.2)
New database connection attempts to Oracle database 11gR2 fail with following Oracle error:
Listener refused the connection with the following error: ORA-12519, TNS:no appropriate service handler found [SQLCode: 12519], [SQLState: 66000] None None