Oracle Process Structure

Oracle takes advantage of various types of processes:

—User process: Started at the time a database user requests connection to the Oracle server

—Server process: Connects to the Oracle instance and is started when a user establishes a session

—Background processes: Started when an Oracle instance is started

User Process: A progrm that requests interaction with the Oracle server, Must first establish a connection, Does not interact directly with the Oracle server.

Server Process: A program that directly interacts with the Oracle Server

—Fulfills calls generated and returns results

—Can be deficated or shared server

IPC: Inter Process Communication,包括共享内存、队列、信号量等几种形式。

Background Process

Maintains and enforces relationships between physical and memory structures:

—Mandatory background processes

DBWn PMON CKPT LGWR SMON

—Optional background processes

ARCnLMDnQMNnCJQ0LMONRECODnnnLMSSnnn

LCKnPnnn

DBWn(Database Writer), DBWn writes when:

—Checkpoint occurs

—Dirty buffers reach threshold

—There are no free buffers

—Timeout occurs

—RAC ping request is made

—Tablespace OFFLINE

—Tablespace READ ONLY

—Table DROP or TRUNCATE

—Tablespace BEGIN BACKUP

Log Witer(LGWN), LGWR writes:

—At commit

—When one-third full

—When there is 1MB of redo

--Every three seconds

--Before DBWn writes

System Monitor(SMON)

Responsibilities

—Instance recovery

—Rolls forward changes in noline redo log files

—Opens database for user access

—Rolls back uncommitted transactions

—Coalesces free space

—Deallocates temporary segments

Process Monitor(PMON),Cleans up after failed processes by:

—Rolling back the transaction

—Releasing locks

—Releasing other resources

—Restarting dead dispatchers

Checkpoint(CKPT): Responsible for:

—Signaling DBWn at checkpoints

—Updating datafile headers with checkpoint information

Archiver(ARCn)

Automactically archives online redo file

Logical Structure

—Dictates how the physical space of a database is used

—Hierarchy consisting of tablespaces(可以包括多个数据文件), segments(同), extents(只能在一个数据文件中)and blocks(8K)

DB Administration Tools

1.Oracle Universal Installer

2.Database Configuraation Assistant

3.Database Upgrade Assistant

4.Oracle Net Manager

5.Oracle Enterprise Manager

6.SQL*Plus

7.Recovery Manager

Oracle Univeral Installer

Used to install, upgrade, or remove software

Based on a Java engine

Features include

Automatic dependency relolution

Allows for Web-based installations

Tracking inventory of component and suite installations

Deinstallation of installed components

Support for multiple Oracle homes

Support for globalization technology

Oracle DBCA

You use the Oracle Database Configuration Assistant to:

—Create a database

—Configure database options

—Delete a database

—Manage templates

DB Administrator Users

Users SYS and SYSTEM are created automatically

—During database creation

—Granted the DBA role

User SYS

—Owner of the database data dictionary

—Default password : change_on_install

User SYSTEM

—Owner of additional internal tables and view used by Oracle tools

—Default password: manager

SQL*Plus

An Oracle tool providing

—Capability to interact with and manipulate the database

—Ability to start up and shut down the database, create

and run queries, add rows, modify data, and write customized reports

A subset of the standard SQL language with specific add ons

Oracle Enterprise Manager

Initialization Parameter Files

—Entries are specific to the instance being started

Two types of parameters:

—Explicit: Having an entry in the file

—Implicit: No entry within the file, but assuming the Oracle default values

Multiple initialization parameter files can exist

Changer to entries in the file take effect based on

the type of initialization parameter file used:

—Static parameter file, PFILR

—Persistent server parameter file, SPFILE

PFILE –initSID.ora

—Text file

—Modified with an operating system editor

—Changes take effect on the next start up

—Only opened during instance start up

—Default location is $ORACLE_HOME/dbs

Oracle SID

the SID is a site identifier. It and ORACLE_HOME(where the Oracle software is installed) are hashed together in UNIX to create a unique key name for attaching an SGA.If your ORACLE_HOME is not set correctly, you’ll get the ORACLE NOT AVAILABLE error.

SPFILEspfileSID.ora

Binary file

Maintained by the Oracle server

Always resides on the server side

Ability to make changes persistent across shutdown and startup

Can self-tune parameter values

Can have Recovery Manager support backing up to the initialization parameter file

Spfile.ora和file.ora可以相互转化：

create spfile from pfile; strings spfile |more(提取二进制中的可读字符串打印出来)

Modify Parameters in SPFILE

Alter system set parameter name =value

find command

show parameter pram name;

SPFILE vs PFILE

1.An SPFILE can be backed-up with RMAN(RMAN cannot backup PFILES)

2.Reduce human errors.The SPFILE is maintained by the server. Parameters are checked before changes are accepted.

3.Eliminate configuration problems (no need to have remote machine)

4.Easy to find –stored in a central location

SPFILE is better than PFILE!