The document provides an overview of Oracle 10g database architecture including its physical and logical structures as well as processes. Physically, a database consists of datafiles, redo logs, and control files. Logically, it is divided into tablespaces containing schemas, segments, and other objects. The Oracle instance comprises the system global area (SGA) shared memory and background processes that manage tasks like writing redo logs and checkpointing data blocks. User processes connect to the database through sessions allocated in the program global area.

1. Introduction to
Oracle 10g Database
Eryk Budi Pratama

2. Agenda
• Review SQL Statements
• Oracle Architecture (Physical Structure)
• Oracle Architecture (Logical Structure)
• Oracle Instance
• User Process
• Program Global Area (PGA)
• System Global Area (SGA)
• Oracle Background Process

3. Review
• Data Definition Language
• Data Manipulation Language
• Data Control Language

5. PL/SQL
• PL/SQL is a powerful extension to SQL that not
only adds condition testing, looping, and
exception handling, but also allows developers
to write application-specific functions,
procedures, packages, and triggers

10. Oracle Server Architecture

11. Oracle 10g Physical Structure

12. Physical Structures
• Datafiles (*.dbf)
The datafiles contain all the database data. The data of logical
database structures, such as tables and indexes, is physically stored
in the datafiles allocated for a database
• Control Files (*.ctl)
A control file contains entries that specify the physical structure of
the database such as Database name and the Names and locations
of datafiles and redo log files
• Redo Log Files (*.log)
The primary function of the redo log is to record all changes made to
data. If a failure prevents modified data from being permanently
written to the datafiles, then the changes can be obtained from the
redo log, so work is never lost

13. Physical Structures (cont.)
• Archive Log Files (*.log)
• Oracle automatically archives log files when the database is in
ARCHIVELOG mode. This prevents oracle from overwriting the
redo log files before they have been safely archived to
another location.
• Parameter Files (initSID.ora)
• Parameter files contain a list of configuration parameters for
that instance and database.
• Alert and Trace Log Files (*.trc)
• Each server and background process can write to an
associated trace file. When an internal error is detected by a
process, it dumps information about the error to its trace file.

15. Oracle 10g Logical Structure

16. Logical Structures
• Tablespace
A database is divided into logical storage units called
tablespaces, which group related logical structures together.
One or more datafiles are explicitly created for each
tablespace to physically store the data of all logical structures
in a tablespace.
• Data Blocks
At the finest level of granularity, Oracle database data is stored
in data blocks. One data block corresponds to a specific
number of bytes of physical database space on disk.

17. Logical Structures (Cont)
• Extents
An extent is a specific number of contiguous data blocks,
obtained in a single allocation, used to store a specific type of
information.
• Segments
A segment is a set of extents allocated for a certain logical
structure. The different types of segments are :
1.Data segment – stores table data
2.Index segment – stores index data
3.Temporary segment – temporary space used during SQL
execution
4.Rollback Segment – stores undo information

18. • Schema
A schema is a collection of database objects. A schema is
owned by a database user and has the same name as
that user. Schema objects are the logical structures that
directly refer to the database's data. Schema objects
include structures like tables, views, and indexes

20. The Oracle Server architecture can be described in three
categories:
•User-related processes
•Logical memory structures that are collectively called an
Oracle instance
•Physical file structures that are collectively called a
database

21. Oracle Instance
An Oracle database server consists of an Oracle database
and an Oracle instance. Every time a database is started, a
system global area (SGA) is allocated and Oracle
background processes are started. The combination of the
background processes and memory buffers is called an
Oracle instance.

23. User Processes
• User Processes initiates connection
• Maintaining connection in a session

25. Program Global Area (PGA
• PGA is a memory buffer that contains data and control
information for a server process
• PGA is created by oracle when a server process is started
• PGA area is a non-shared area of memory created by
oracle when a server process is started.

27. System Global Area (SGA)
• System Global Area (SGA) is a shared memory region
that contains data and co ntrol information for one
Oracle instance
• Oracle allocates the SGA when an instance starts and
deallocates it when the instance shuts down
• Each instance has its own SGA

28. SGA Memory Structure
• Buffer Cache
Database buffers store the most recently used blocks of
data. The set of database buffers in an instance is the
database buffer cache.
• Redo Log Buffer
Redo log buffer stores redo entries—a log of changes
made to the database
• Shared Pool
Shared pool contains shared memory constructs, such as
shared SQL areas

29. Oracle Background Process
An Oracle database uses memory structures and processes
to manage and access the database. All memory structures
exist in the main memory of the computers that constitute
the database system. Processes are jobs that work in the
memory of these computers.

30. Oracle Background Process
(cont.)
• System Monitor – SMON
• This database background process performs instance
recovery at the start of the database. SMON also
cleans up temporary segments that are no longer in
use and recovers dead transactions skipped during
crash and instance recovery because of file-read or
offline errors. It coalesces i.e. combines contiguous
free extents into larger free extents.
• Process Monitor - PMON
• This database background process cleans up failed
user processes. PMON is responsible for releasing the
lock i.e. cleaning up the cache and freeing resources
that the process was using. Its effect can be seen
when a process holding a lock is killed.

31. Oracle Background Process
(cont.)
• Database Writer - DBWR
• This background process is responsible for managing
the contents of the data block buffer cache and
dictionary cache. DBWR performs batch writes of
changed block. Since Oracle uses write-ahead logging,
DBWR does not need to write blocks when a
transaction commits.
• Recover - RECO
• The recover process automatically cleans up failed or
suspended distributed transactions.

32. Oracle Background Process
(cont.)
• Log Writer - LGWR
• This background process manages the writing of the
contents of the redo log buffer to the online redo log files.
LGWR writes the log entries in batch form. The Redo log
buffers entries always contain the most up-to-date status
of the database.
• Archiver - ARCH
• The Archiver process reads the redo log files once Oracle
has filled them and writes a copy of the used redo log files
to the specified archive log destination(s). Actually, for
most databases, ARCH has no effect on the overall system
performance. On some large database sites, however,
archiving can have an impact on system performance.

33. Oracle Background Process
(cont.)
• Checkpoint - CKPT
• All modified information in database buffer in the SGA is written
to the datafiles by a database write process (DBWR). This event
indicates a checkpoint. The checkpoint process is responsible for
signaling DBWR at checkpoints and updating all of the datafiles
and control files of the database.
• Job Queue Processes
• Job queue processes are used for batch processing. They run user
jobs. They can be viewed as a scheduler service that can be used
to schedule jobs as PL/SQL statements or procedures on an
Oracle instance. Given a start date and an interval, the job queue
processes try to run the job at the next occurrence of the
interval.

34. Q&A