Introduction to the basic structure of Oracle Database learning _oracle

To generalize Oracle's basics, to sum up, Oracle is made up of instances and databases. The structure is as follows:

An Oracle database consists of an instance, a database:

* The database consists of data files (including Oracle data, index, table structure, etc., control files (including operational information for each table), log files (data manipulation SQL statements), parameter files, password files, log archives (in archive mode) (server crashes, hard disk damage, Used by log recovery

* An instance consists of a memory structure (memory STRUTCT) and a background process (background processor).

The memory structure consists of:

* Pga:processor Global area, each client access to the Oracle server has a PGA for saving information about the customer order

* Sga:system Global area system, mainly for Oracle instances, including shared pool, data buffer region, redo log buffer.

Shared pool:

* Including the library cache, data directory cache composition, where the library cache mainly save the most recent SQL inspection, compilation, execution plan, the next time the same statement over, you can reuse these, to avoid duplication of the inspection compiled execution plan. Data Directory cache mainly saves the database data table's field definition, index data and so on, the shared pool size directly affects the database performance.

Data buffer area: Mainly save the user's modification of the information, query operation. The size of the memory area directly affects the performance of the database.

Redo Log Buffer area: Mainly saves the recent user to the database operation record, this size does not have the big influence to the database performance

The background processes that Oracle must have include: Pmon, Smon, DBWR, LOGWR, CKPT, and so on, each of the following functions:

*pmon monitors the PGA's health, releases the already dead PGA, reclaims resources, and manages the PGA lifecycle

*smon Monitor the SGA's health, collect SGA fragment memory, and monitor instance health

*DBWR maintains consistency of data buffer area and physical tables

*LGWR maintains redo log buffer area memory data and log file consistency

*CKPT sets the checkpoint, which can revert to the instance before it fails if there is a problem with the Oracle instance.

Oracle memory structure consists of block, region, segment, TABLESPACE, block is Oracle in memory, the smallest structure, region, segment, Tablespace is Oracle in turn up memory structure. Fast too small data management trouble, too large, more data fragmentation. Concrete analysis of the specific situation.

Tablespace is the largest logical unit of Oracle, a tablespace can belong to only one database, and a database may contain more than one tablespace, but by default it contains a system's table space. To create a table space syntax:

Copy Code code as follows:

CREATE tablespace Name
datafile path [SIZE interger m| K
LOGFILE Path
[Autoextend on | OFF]

Client-linked server configuration:

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