Oracle Architecture Detailed ____oracle

Oracle architecture is built around this diagram, and to get an insight into Oracle, you have to figure it out.

As shown in figure:

First, the basic composition:

Oracle Server:

Typically a instance and a database

1 instance can only correspond to one database.
Special: 1 databases can have multiple versions of the database software on one server at a time, each database software can build multiple databases, but each database corresponds to only one instance, and it can be understood that there is only one SID per database instance.                                                                          Each library built with DBCA is relatively independent, and if you create multiple libraries on the same server, you must differentiate the parameter files for the environment variables, and you need to do the following when switching instances: Connect user name/password @ Instance service name

Oracle Instance:

is made up of memory (SGA) and background processes (Backupground process)

Access to the database through instance

One instance can open only one database

Oracle Database:

Data files:

Data files always store database data, including data dictionaries, user data (tables, indexes, clusters), undo data, etc.

Redo logs (Redo log):

"Write First and then"

Redo logs are used to record changes to the database and need to use redo logs for routine recovery or media recovery

When a DDL or DML operation is performed, the change of Things is written to the redo log buffer, and at a specific time LGWR writes the contents of the redo log buffer to the redo log.

Controlling files (Control file)

Control files are used to record and maintain the physical structure of the database, and each Oracle database must contain at least one control file.

Archive log (Archive log):

A backup of the inactive (Inactive) redo log.

Password files (Password file):

Used to authenticate privileged users (special database users with SYSDBA, sysoper permissions)

Parameter files (Parameter file):

Used to define initialization parameters required for the startup instance, including text parameter files (pfile) and server parameter files (spfile)

User and Server process:

The process that occurs when an SQL statement is executed, with each connection, Oracle server creates a session, generates a server process, and generates a user process when the client initiates a connection.

Architecture can be divided into database structure and instance structure.

The following structure:

II. detailed structure of instance

1. Memory structure

Mainly includes SGA (System global Area) and PGA (Program global Area)

The PGA is used for server process (not included in the instance, not focused discussion) when the program is up.

The SGA (System Global area) consists of a set of memory structures that are shared by all user processes in a single area of memory. When the routine is started, Oracle automatically allocates the SGA, and when the routine is closed, Oracle automatically frees up the memory space occupied by the SGA.

Here's Dave. About the SGA detailed:

http://blog.csdn.net/tianlesoftware/article/details/5594080

The SGA includes the share pool,db buffer Cache,redo log buffer,large Pool,java pool.

We all know in 9i that when using dynamic SGA in Oracle management, the size of the granule is related to the size of the SGA.

The smallest unit allocated by the SGA is a granule. The size of the Oracle SGA is always granule multiple times, that is, allocations are allocated with an integer granule.

The rules in 9i are as follows:

Linux/unix

SGA <=128 M granule 4M

SGA >128m granule 16M

Windows

SGA <=128 M granule 4M

SGA >128m granule 8M

The allocation rule in 10g is

Linux/unix

SGA <=1g granule 4M

SGA >1g granule 16M

Windows

SGA <=1g granule 4M

SGA >1g granule 8M

Sql> Select Component, granule_size from v$sga_dynamic_components;

COMPONENT granule_size

---------------------------------------------------------------- ------------

Shared Pool 4194304

Large Pool 4194304

Java Pool 4194304

Streams Pool 4194304

DEFAULT Buffer Cache 4194304

KEEP Buffer Cache 4194304

Recycle buffer Cache 4194304

DEFAULT 2K Buffer Cache 4194304

DEFAULT 4K Buffer Cache 4194304

DEFAULT 8K Buffer Cache 4194304

DEFAULT 16K Buffer Cache 4194304

DEFAULT 32K Buffer Cache 4194304

ASM Buffer Cache 4194304

Rows selected.

elapsed:00:00:00.06

Sql>

sql> desc v$sga_dynamic_components;

Name Type

--------------------------------------------------------

COMPONENT VARCHAR2 (64)

Current_size number

Min_size number

Max_size number

User_specified_size number

Oper_count number

Last_oper_type VARCHAR2 (13)

Last_oper_mode VARCHAR2 (9)

Last_oper_time