Learn 25 basic and common Oracle database knowledge

The following articles mainly introduce 25 basic common knowledge about Oracle databases, which plays an important role in practical application, the following articles describe the 25 basic common knowledge of Oracle databases. I hope you will gain some benefits.

1. a tablespace can belong to only one database.

2. Each database has at least one control file. We recommend that you store three files on different disks ).

3. Each database has at least one tablespace SYSTEM tablespace ).

4. 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.

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

6. A data file can belong to only one tablespace.

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

8. Create a new data file to create a new tablespace.

9. The data file is formatted as an ORACLE block by ORACLE. In versions earlier than Oracle9i, the size of the ORACLE block is set during the first database creation.

10. The database cannot be changed in the future. To change the database, you must recreate the database.

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

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

13. The sum of PCTFREE and PCTUSED cannot be greater than or equal to 100.

14. A single transaction cannot span multiple rollback segments.

15. The index table does not contain the ROWID value.

16. rollback segments of different sizes have no benefit.

17. After COMMIT, the data may not be immediately written to the disk data file ).

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

19. In Oracle 8.0.4, the default database created during initial installation is named ORCL.

20. The maximum length of a block is 16 KB (2 K, 4 K, 8 K, 16 K ).

The maximum number of files in each database is in block size)

2 K block, 20000 files

4 K block 40000 files

8 K or more 65536 files

21. oracle server can start multiple databases at the same time.

22. multiple versions of ORACLE Database systems can be installed on one operating system, which is UNIX, but not NT ).

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

24. Each Oracle database has one database INSTANCE) except OPS ).

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

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