Oracle Logical Structure (2) Related data dictionary

1. Introduction to Basic table space

A. system table space

Main storage data dictionary and Internal system table base table

To view the SQL of the Data data dictionary

SELECT * FROM Dict

To view the SQL for an internal system table

SELECT * FROM V$fixed_view_definition

DBAs must have a deep understanding of the data dictionaries in the system's system tables, and they must prepare some basic SQL statements that allow you to immediately understand the state of the system and the status of the database, including:

The remaining space of the system

The SGA of the system

Waiting for the state system

User's permissions

Current User lock

Usage of buffer and so on

On the way to being a DBA, we do not recommend that you rely too much on good database management tools such as Oem/quest, because they are not conducive to your understanding of the data dictionary, and SQL statements can do almost all of the database management work.

A large amount of reading a small amount of writing is a significant feature of the table space.

B. temporary table space.

Temporary table spaces, as the name suggests, are used to hold temporary data, such as temporary space for a sort operation, and his space will be released at the next time the system starts.

C. Roll back segment table space

I. The role of the rollback segment in the system

When the database is updated insert delete operation, the new data is updated to the original data file, and the old data (before Image) is placed in the rollback segment, if the data needs to be rolled back, then the data can be copied from the rollback segment to the data file. To complete the rollback of the data. When the system is restored, the rollback segment can be used to rollback data that is not being commit, and to resolve one of the systems.

When a rollback segment is a large number of writes, typically a small amount of read, it is recommended that the rollback segment be placed alone on a separate device, such as a separate disk or RAID, to reduce disk IO contention.

Ii. mode of operation of the rollback section

A rollback table space can be divided into multiple rollback segments.

A rollback segment can hold data for multiple sessions.

The rollback segment is a circular data model

It is assumed that the rollback segment is composed of 4 intervals, and their use order is interval 1à interval 2à interval 3à interval 4à interval 1. That is, the interval can be recycled, when the interval 4 to the interval of 1, the interval 1 inside the session has not ended, interval 4 can not be used after the interval 1, then the system must allocate interval 5, to continue to serve other sessions.

We analyze the completion of an UPDATE statement

①. User submits an UPDATE statement

②. Server Process checks memory buffering.