A database can be designed as a multitenant container database (CDB) or a non-container database (non-CDB)
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 maximal length of the database name is eight
ASCII characters (or bytes).
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Starting with 9i, bitmaps (which then superseded free lists) are used to track free and used blocks in segments.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
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;