I tried to connect to an Oracle database through SQL*Plus and all of a sudden I get the following errors:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Please advise because it's affecting our production.
I would definitely say that your production is being affected! The ORA-1034 error means that Oracle is not up and running on your server. So the DBA needs to start the database. Once Oracle is up and running, you will be able to connect to it.
Next, I would try to figure out why the database is no longer running. The first place to look is in your BACKGROUND_DUMP_DEST directory, which contains your Alert Log. The Alert log will give you reasons why the database crashed. You may also find relevant trace files in that same directory. There are too many reasons why this could be happening, so you'll have to consult the log to find out the exact reason.
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