Logical and physical databases in Oracle

Logical and physical databases in Oracle

Oracle abstracts the logical storage structure to adapt to different underlying physical structures. There are two advantages:

(1) so that Oracle users only need to understand the data logic and do not feel the existence of the physical layer, nor do they have to understand any details about the physical storage structure.

(2) For other OS users (including system administrators), only the OS physical files are visible and the internal logic of the data is not understood.

Of course, there must be some correspondence between the logical database and the physical database, which is exactly what the DBA needs to do.

1 physical database

Oracle databases include three types of physical files: control files, online redo log files, and data files. These files are physical files that have different implementations on different operating system platforms.

Note: parameter files, control files, password files, archive log files, alarm logs, and tracing files are required for Oracle startup and loading. However, strictly speaking, they are not part of the database.

2. logical database

Tablespace, segment, interval, and Oracle block.

3 logical and physical Mappings

This ing relationship is implemented through the control file and data dictionary.

3.1 startup phase

Before starting a database, you must use an external file to find the corresponding relationship. The instance first finds the "control file" through the "parameter file", and then passes

The "control file" is used to identify the data files in the SYSTEM tablespace.

3.2 running stage

After the SYSTEM tablespace is found, the Oracle database has been loaded, and subsequent mappings will be searched in the data dictionary in the tablespace.

In this case, the database is able to manage itself and no longer depends on external files.

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