I - Oracle 10g
Oracle 10g: ‘g’ stands for ‘Grid’, the advance of this infrastructure give us the following benefits:

• Low Cost
• High quality of Service
• Easy to manage though Oracle tools

II – Oracle 10g Infrastructure
Oracle 10g Database contains of 2 parts:
1. Oracle 10g Instance:
All things that run, and do all function that Oracle does. Oracle Instance is like ‘soft’ part

Structure of Oracle 10g Instance:

• SGA( System Global Area): is a chunk of memory that is allocated by an Oracle Instance and is shared among Oracle processes,. It contains all sorts of information about the instance and the database that is needed to operate.
• Structure of SGA:
• Shared Pool: is the most important area of the SGA, except for the data buffer caches, used by Oracle for 3 main purposes:
• Library cache – The library cache contains the current SQL execution plan information. It also holds stored procedures and trigger code.
• Dictionary cache - The dictionary cache stores environmental information, which includes referential integrity, table definitions, indexing information, and other metadata stored within Oracle's internal tables.
• Session information – Systems that use SQL*Net version 2 with a multi-threaded server need this area to store session information. Beginning with Oracle9i, the v$session view contains information related to Oracle*Net users.
• Streams Pool: New to Oracle 10g, it provides buffer area for streams components of Oracle.
• Java Pool: Used for Java applications, java code …
• Database Buffer Cache: buffers data from Oracle datafiles, so it will fasten I/O and improve performance
• Redo log buffer: provide buffer to records all changes in the datafiles.
• Large Pool: provide memory for rman, PQ message buffers.

• PGA(Program Global Area): is a memory region containing data and control information for a single process (server or background). One PGA is allocated for each server process; the PGA is exclusive to that server process and is read and written only by Oracle code acting on behalf of that process. A PGA is allocated by Oracle when a user connects to an Oracle database and a session is created.

There are 3 kinds of process in Oracle 10g .

• User Process: start at client side, when a user connects to Oracle Server. It helps User do everything to the server
• Server Process: handle the requests of user processes connected to an instance. There are 2 modes of server process:

• Dedicated server process: One Server process service one user process –  available when server is in dedicated mode
• Shared server process: One Server process service many user processes. – Available when server is in shared mode

• Background process: run and manage the Oracle instance. There are many kinds of Background processes, and can be accesses though v$session with type = ‘BACKGROUND’. Below is some of the Oracle Processes.

• Database writer(DBWn): Write data from Database buffer cache into disk
• Log writer (LGWR): Write data from Redo log buffer into Redo log file
• Archiver (ARCn): Write data from Redo log file into Archive log file
• Check point ( CKPT): Write check point information into control files, datafile header, archive log file.
• SMON: recovers after instance failure and monitors temporary segments and extents.
• PMON: process recovers failed process resources.

2. Oracle 10g Database:
All things that is stored in the hard disk that Oracle manages. Oracle Database is like ‘physical’ part
There are 6 kinds of files that Oracle 10g manages. They are:

• Control files: store the status of the physical structure of the database. This file is the most important file in oracle files
• Data files: The file that store data of Oracle
• Online Redo Log files: Record changes of Data into log file.
• Archive Log files: store data from Online Redo Log file
• Parameter file: store initialization parameters of Oracle
• Backup files: All backup files from RMAN
• Password file: Store the password out of Database. If the remote_login_passwordfile initialization parameter is set  to SHARED or EXCLUSIVE