Basic Oracle knowledge

A tablespace can belong to only one database.

Each database must have at least one control file (we recommend that you store three files on different disks)

Each database has at least one tablespace (system tablespace)

The purpose of creating a system tablespace is to store tables with the same purpose as much as possible to improve the efficiency of use. Only data dictionaries should be stored.

Each database has at least two online log groups, and each group has at least one online log file.

A data file can belong to only one tablespace.

Once a data file is added to a tablespace, it cannot be removed from the tablespace or be added to other tablespaces.

To create a new tablespace, you must create a new data file.

The data file is formatted as an oracle block by Oracle. In versions earlier than Oracle9i, the size of the Oracle block was set when the database was created for the first time,

And it cannot be changed in the future. To change it, you can only recreate the database.

A Segment segment can belong to only one tablespace, but can belong to multiple data files.

A zone extent can belong to only one data file, that is, the range (extent) cannot span data files.

The sum of pctfree and pctused cannot be greater than or equal to 100

A single transaction cannot span multiple rollback segments.

The index table does not contain the rowid value.

Rollback segments of different sizes have no benefit

After commit, the data may not be immediately written to the disk (data file)

A transaction is written to the redo log even if it is not committed.

The default database created during initial installation in Oracle 8.0.4. The instance name is orcl.

The maximum length of a block is 16 KB (2 k, 4 K, 8 K, 16 K)
Maximum number of files per database (by block size)
2 K block, 20000 files
4 K block 40000 files
8 K or more 65536 files

Oracle server can start multiple databases at the same time

Multiple versions of Oracle Database systems can be installed on one operating system (either Unix or NT)

A set of Oracle Database Systems can contain multiple Oracle databases and their corresponding instances.

Each Oracle database has one database instance (excluding OPS)

Therefore, multiple Oracle database instances can be started on one operating system at the same time.