We have Oracle9i installed on Windows 2000 Server. There are two instances configured, and they were running properly without any problem. But one day suddenly when I tried to connect to one of them, it gave me an error:
ERROR: ORA-01034: ORACLE not available ORA-27101: shared memory realm does not exist
This error was for both the instances. I checked the services panel, and all the services were running, and they were set to auto start. I restarted the services, and I did not get the error for some time, like 2-3 hours. But I again got the same error, and I am not able to understand why I am getting this error all of a sudden. Can you please help?
The first thing to check is that your environment is set up correctly to connect to the instance that is giving you problems. This means that your session will have to have ORACLE_SID, ORACLE_HOME and PATH set correctly to be able to connect locally. If you are connecting through a TNS alias, make sure your TNSNAMES.ORA file is configured properly to point to each instance on that server.
The next thing to check is to ensure that your database has not crashed. You will want to look in your instance's Alert Log. This log can be found in the directory denoted by your instance's BACKGROUND_DUMP_DEST initialization parameter. Your Alert Log will show if the instance crashed and give a clue as to why it crashed. It may point to other trace files with more information. Without looking at your Alert Log, it can be too many reasons to guess as to why your instance is crashing.
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