Oracle Database

Database name

When a database is created, it can or will be given a database name.

This name is stored (among other information) in the database's control files.

The database name must match the value of the db_name init parameter.].

The maximal length of the database name is eight ASCII characters (or bytes).

Database ID

When a database is created, Oracle calculates a numerical database identifier (DBID).

Physical and logical storage structures

An Oracle database consists of physical and logical components.

Physical components (files)

The physical components are files in a file system. These files store

data and
metadata.

The data is what is precious to a user. It is inserted, updated and deleted with DML statements and queried with select statements.

The metadata stores information about the database server. It is used by the instance for proper operation.

The physical files are

The physical files are created with the create database statement. Additional data files can later be added.

Logical structures

Logical components are not visible in the operating system. They are

Opening a database

A database cannot be opened if online data needs media recovery.

Tablespace

The physical data files that store the data is logically abstracted by tablespaces. That is, a tablespace represents one or more data files.

Protected database

A protected database is a database that backs up to a Recovery Appliance.

CDB

A CDB consists of

One CDB root container (also the root, named CDB$ROOT)
exactly one seed pluggable database (aka seed PDB, named CDB$SEED)
zero or more user-created pluggable databases (PDBs), and
zero or more application containers

The entire CDB ecosystem is referred to as the system container.

To a user or application, PDBs appear as separate databases.

Space management

Starting with 9i, bitmaps (which then superseded free lists) are used to track free and used blocks in segments. b

dba_free_space, dba_free_space_coalesced.

dbms_space

View free and used/occupied space in a tablespace:

select
   file_id,
   block_id block,
   block_id + blocks next_block,  
   blocks,
   segment_name,
   partition_name,
   segment_type
from (
   select file_id, block_id, blocks, segment_name, partition_name, segment_type from dba_extents      where tablespace_name = '...' union all
   select file_id, block_id, blocks, null        , null          , null         from dba_free_space   where tablespace_name = '...'
)
order by
   file_id,
   block_id desc;

Misc

A database maintains a list of database users.

Creation of a database

When a database is created, the SYSTEM, SYSAUX and TEMP (a temporary tablespace) is created with it.