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I'm learning Oracle and below is my testing of starting up an Oracle instance and make the database available.

oracle:[~]$ sqlplus

SQL*Plus: Release 19.0.0.0.0 - Production on Mon Aug 5 09:29:30 2019
Version 19.3.0.0.0

Copyright (c) 1982, 2019, Oracle.  All rights reserved.

Enter user-name: sys as sysdba
Enter password:
Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area 1207955552 bytes
Fixed Size                  9134176 bytes
Variable Size             469762048 bytes
Database Buffers          721420288 bytes
Redo Buffers                7639040 bytes
Database mounted.
Database opened.
SQL>

As I understand, database is a bunch of files on disk. The startup command creates an instance and mounts and opens the database, which makes it available for users. My questions is:

  • Without an instance, the only thing left is a bunch of files, the database. I use sqlplus logged in and created an instance. How does the authentication process work? Does sqlplus manage this process? Since when the logging happens, no instance exists and the database at that time is still a bunch of unusable files.
  • When I run startup, a instance will be created and it will mount to my database and open it. How does it know which database it should mount and open? I didn't specify some information about the database name etc. here.

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