Nine sister to take you to understand Oracle

I. Oracle Architecture

Oracle 's architecture is the composition of the database, the work process, and the organization and management of data in the database, to understand The architecture of the Oracle database, you must understand the Oracle The main components and important concepts. the Oracle architecture includes a range of components, including instances, user processes, service processes, data files, and other files, such as parameter files, password files, and archive log files. As shown in the following:

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instances and databases are the core component of the Oracle database architecture is also the two most important concepts,and the main task of theDBA is to maintain the instance and database.

1) Example

An instance is a collection of background processes and memory that must be started to access data in the database.

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N When Oracle starts, a system global zone (SGA) is assigned and a series of Oracle background Processes are started

N An instance can only open and use one database

N Oracle is divided into single-process and multi-process instances, and is now generally a multi-process instance, multi-process is multi-user, different users use different processes to execute different parts of Oracle.

2) Database

A database is a collection of data that is treated as a logical unit.

The Oracle database consists of operating system files that provide the actual physical storage for database information

Oracle databases include logical and physical structures.

Physical Structure: Refers to a set of operating system files that store database information, each with a logical structure and a physical structure. A physical structure is a set of operating system files that comprise a database, consisting mainly of 3 types of files: Data files, control files, and redo log files.

Logical structure: Refers to the logical storage structure of database data, including: Table space, data segment, table, view, etc.

ii.Oracle Storage Architecture

Oracle 's storage structure is divided into physical and logical structures, both of which are independent and interlinked.

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Three.

1. Physical Structure:

The physical structure is the operating system physical file used after the Oracle database was created, divided into the following two types:

1) Main documents

N data files: Data files are physical storage database files, data file characteristics: Each data file is only associated with a database, a table space can contain one or more data files, a data file can only belong to one table space. The data file contains user or application data for the database, as well as metadata and data dictionaries.

N Redo log file: It records all changes to the data and provides a data recovery mechanism that, if the database server crashes but does not lose any data files, the instance can use the information in these files to recover the database.

N Control File: When the database reads, the data file is located according to the information of the control file. The control file stores the name and location of the data file and the redo log file. A database of at least two control files,oracle11g By default includes 3 control files, each control file content is the same, you can avoid because of a control file corruption caused the database cannot be started. The control file records the following key information: the location and size of the data file, the location and size of the redo log file, the database name and creation time, and the log sequence number. Control files are critical to the database. Without these files, you cannot open the data file to access the data in the database.

2) Other Files

N parameter file: Used to define the configuration at instance startup

N password file: Allow sysdba,sysoper , and sysasm to connect remotely to the instance and perform administrative tasks

N Archive log files: Using these files and database backups, you can recover lost data files. That is, the archive log can restore the restored data file

2. Oracle Logical Structure

Oracle 's logical components include table spaces, segments, extents, blocks, and schemas.

1) Table Space

N The tablespace is the largest logical unit in the database, and the SYSTEM and sysaux table spaces are the table spaces that must exist when the database is created and the TEMP ,USERS , and so on.

N Each tablespace is made up of one or more data files, and a data file can be associated with only one table space.

N the size of the tablespace equals the sum of all the data file sizes that make up the tablespace.

N table space and data files are relative, if there is no data file, table space can not exist independently, if only table space does not have a data file is not good, like if the computer does not have a hard disk, you can no longer logically see C disk D disk, where the hard drive is the equivalent of a data file, and C disk is the equivalent of a table space. We can make multiple data files into a table space, and then store the data in the table space, the table space and data files are corresponding, a table space can be composed of one or more data files, but a data file can only be in one table space .

The role of Table spaces:

N for different users to assign different table space, different schema objects are assigned different table spaces, which facilitates the management of user actions and schema objects.

N Different data files can be created on different disks, which facilitates managing disk space, improving I/O performance, backing up and recovering data, and more.

n   oracle data for the system's internal tables and data dictionaries, such as indicated, column names, User name, and so on.

n   system staspack logminer etc.) data used. Object data for storing various patterns, such as smart Proxy user dbsnmp ODM etc.

N Users table space: As a table space for users, you can create various objects on this table space, such as creating tables, indexes, and so on.

N TEMP tablespace: A special table space for temporary data, for example: when sorting is required, the system will temporarily store the sorted data in that tablespace, and once the sorting process is complete, the space occupied by the sort data can be released, called a temporary tablespace.

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Nine sister to take you to understand Oracle