Oracle Getting Started notes-start advanced

Source: Internet
Author: User

1.2 Advanced Content:

Two concepts: SCN and Checkpoint

Definition of 1.SCN:

System change member, which is a very important data structure in the database.

The SCN is used to indicate the version submitted by the database at a specific time. When a transaction commits, it is given a unique SCN that identifies the transaction. The SCN is also used as the internal clock mechanism of the Oracle database, and can be seen as a logical clock, with each database having a global SCN generator.

As a logical clock inside the database, database transactions are sorted by SCN, and Oracle also implements important database functions such as consistent read consistency based on the SCN. In addition to distributed transactions (distributed transactions), the SCN is also extremely important.

The SCN is unique in the database and increases over time, but may not be consistent. The value of the SCN will never be reset to zero unless the database is rebuilt.

Oracle Getting Started notes-start advanced

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