oracle basics

7/29/2019 Oracle Basics

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- Kishore Soma

Oracle BasicsSAPs perspective


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Contents

Oracle History

Oracle architecture

DB Startup options

DB shut down options

Database mode

Backup types

Limitations of Oracle database Troubleshooting tips

References


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Oracle History

History of Oracle

1977Larry Ellison and friends founded software Development Laboratory

1979 - SDL changed its company-name to "Relational Software, Inc." (RSI) and introduced itsproduct Oracle V2 as an early commercially-available relational database system

1982: RSI in its turn changed its name, becoming known as "Oracle Corporation",

1984: Oracle Corporation released Oracle version 4, which supported read-consistency.

1985: Oracle Corporation released Oracle version 5, , which supported the client-server model

1988: Oracle RDBMS version 6 came out with support for PL/SQL embedded within OracleForms v3, row-level locking and hot backups.

1989: Oracle Corporation entered the application products market and developed its ERPproduct, (later to become part of the Oracle E-Business Suite

1992: Oracle version 7 appeared with support for referential integrity, stored procedures andtriggers.

1999: The release of Oracle8i aimed to provide a database inter-operating better with the Internet

2001: Oracle9i went into release with 400 new features

2003: Oracle Corporation released Oracle Database 10g. (Thegstands for "grid"; emphasizing amarketing thrust of presenting 10g as "grid-computing ready".)

2005: Oracle Database 10.2.0.1also known as Oracle Database 10g Release 2 (10gR2)appeared

2007: Oracle Corporation released Oracle Database 11g for Linux and for Microsoft Windows.


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Oracle Architecture

Contd.


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Oracle Architecture Contd.,

Oracle Memory structure

Oracles memory structure consists of two memory areas known as:

System Global Area (SGA): Allocated at instance startup, and is a

fundamental component of an Oracle Instance- The parameter used to define SGA is SGA_MAX_SIZE

Program Global Area (PGA): Allocated when the server process is started


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The Oracle database has a logical layer and a physical layer. The physical layerconsists of the files that reside on the disk; the components of the logical layer

map the data to these physical components.

The physical structure

The Logical structure


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Oracle Architechture Contd.,

The Physical Structure

Data files

- 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

- Every Oracle database has a control file. 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

- 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.


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The physical structure (contd.,)

Archive Log Files

- Oracle automatically archives log files when the database is inARCHIVELOG mode. This prevents oracle from overwriting the redo logfiles before they have been safely archived to another location.

Parameter Files

- Parameter files contain a list of configuration parameters for that instanceand database.

Alert and Trace Log Files

- Each server and background process can write to an associated trace file.When an internal error is detected by a process, it dumps informationabout the error to its trace file. The alert log of a database is achronological log of messages and errors.


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Logical Structure

Tablespaces

- 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.

Oracle 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. The standard block size is specified by the DB_BLOCK_SIZE

initialization parameter.


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Logical Structure (contd.,)

Extents

- The next level of logical database space is an extent. An extent is a specific number of

contiguous data blocks, obtained in a single allocation, used to store a specific type of

information.

Segments

- Above extents, the level of logical database storage is a segment. A segment is a set of extents

allocated for a certain logical structure. The different types of segments are :

Data segmentstores table data

Index segmentstores index data

Temporary segmenttemporary space used during SQL execution

Rollback Segmentstores undo information

Schema Overview

- 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.


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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


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Background process- DBWn (DBwriter) This background process is responsible for managing the

contents of the data block buffer cache and dictionary cache. DBWR performsbatch writes of changed block.

- PMONprocess cleans up failed user processes. PMON is responsible forreleasing the lock i.e. cleaning up the cache and freeing resources that the processwas using

- CKPT All modified information in database buffer in the SGA is written to thedatafiles by a database write process (DBWR). This event indicates a checkpoint.The checkpoint process is responsible for signaling DBWR at checkpoints andupdating all of the datafiles and control files of the database.

- LGWRprocess manages the writing of the contents of the redo log buffer to theonline 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.

- Arch The Archiver process reads the redo log files once Oracle has filled themand writes a copy of the used redo log files to the specified archive logdestination(s).

- SMON-process performs instance recovery at the start of the database.SMON also cleans up temporary segments that are no longer in use



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Directory structure of Oracle (As per SAP standards)

There are the following main structures:

$ORACLE_HOME for Oracle-specific objects with the default directory/oracle//

$SAPDATA_HOME for SAP-specific objects with the default directory

/oracle/ Executables with the directory /usr/sap//SYS/exe/run

Oracle Home directory

$ORACLE_HOME/dbs/- spfile.ora: Oracle spfile

- init.ora: Profile for Oracle

- init.sap: Profile for BR*Tools- cntrl.dbf: Database control file

$ORACLE_HOME/bin/ contains binaries such as oracle, sqlplus, exp, imp

rwsr-xr-x ora dba oracle


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Online Redo-Logs directories- /oracle//origlogA/

log_g11m1.dbf

log_g13m1.dbf

- /oracle//origlogB/

log_g12m1.dbf

log_g14m1.dbf

- /oracle//mirrlogA/

log_g11m2.dbf

log_g13m2.dbf

- /oracle//mirrlogB/

log_g12m2.dbf

log_g14m2.dbf

SAPData directories

- sapdata1/

cntrl/cntrl.dbf: Database control file

system_1/system.data1

- sapdata/


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saparch/ - This directory will have the log files of archive log backup takenwith brarchive

sapbackup/ - This directory contains the backup log files, brbackup logs

Sapcheck/ - This directory contains logs of update statistics, checkdb, cleanup

logs, etc

saptrace/- background/

alert_.log: Oracle Alert file

*.trc: Oracle trace files

- usertrace/

*.trc: User trace files

oraarch/: Oracle offline redo log files


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Naming conventi ons of Data F i les

The naming conventions are as follows:

- Directory: /sapdata/_

- File: .data

is the second half of the tablespace name, for example,

UNDO for the tablespace PSAPUNDO. is the sequentially assigned number of the SAP directory in which the data

file will be stored.

is the sequentially assigned number of the data file in thetablespace. The same number also appears in the subdirectory that is createdfor each new file in a tablespace.

For example, the first data file for PSAPUNDO is called:- Directory: /sapdata/undo_1

- File: undo.data1


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Parameter files

Parameter file

init.ora file, which is a normal disk file. It is still used for viewing

by many SAP transactions, so must be kept up-to-date with the newer spfile

(see below).

Spfile.ora, which is a new binary server-side parameter file

introduced by Oracle, available as part of the standard installation from SAP

Web AS 6.40. If your SAP system was upgraded from an older release, you

have to create it yourself initially using SQL*Plus because it was not part of

older SAP installations.


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DB startup options

Type What Happens How

No mount

Database instance is built up

Operating system resources are allocated using configuration

information stored in the profile init.ora or the spfile.

brspace -f dbstart -s nomount

SQL> startup nomount

MountDatabase control files are evaluated.Information about the file structure of the database is read

Data files and logs are not yet opened.

brspace -f dbstart -s mount

SQL> startup mount

Open

All files in the database system are opened.

If required, instance recovery is performed immediately after

opening the database.Pending database transactions are ended.

brspace -f dbstart

SQL> startup
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DB shutdown options

Type What Happens How

Normal

No new database logon possible.

After all database user have logged off, the database is closed

properly: all files are closed, the database is dismounted, and the

instance is shut down.

The database is consistent after shutdown.

brspace -f dbshut -m normal

SQL> shutdown

Immediate

Only the current commands are executed.

PMON ends all sessions and performs a rollback of the open

transactions.The database is then closed properly (as for a normal shutdown).

The database is consistent after shutdown.

DBWR and ARCH might require up to 1 hour post-processing

time.

brspace -f dbshut -m immediate

SQL> shut immediate

Transactional

No new connections are allowed and no new transactions can be

started.

Oracle waits for all open transactions to finish, then disconnects all

users (that is, work processes in the SAP system) and shuts downthe database.

brspace -f dbshut -m transactional

SQL>shut transactional

Abort

Emergency database shutdown

Users are not logged off and open transactions are not rolled back.

The database is notconsistent after shutdown.

An instance recovery is automatically performed at the next

database startup.

brspace -f dbshut -m abort

SQL> shut abort
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Database Modes

Noarchive log mode

In this Mode, there will not be any offline redolog files archived. If the database

is in noarchive log mode, online redo logs can (and will) be overwritten without

making sure they are saved. This implies that a database cannot be recovered even

if backups were made.

Archive log mode

If the database is in archive log mode, the database makes sure that online redo

logs are not overwritten before the have been archived i.e., online redo logs are

archived in this mode
http://www.adp-gmbh.ch/ora/concepts/online_redo_logs.htmlhttp://www.adp-gmbh.ch/ora/concepts/online_redo_logs.html


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Backup Types

OnlineThe starting point of the backup is set using the command ALTER

TABLESPACE BEGIN BACKUP. The header of thetablespace files holds information on the checkpoint and redo log files, that is,the system change number (SCN). When the next redo log file switch orcheckpoint occurs (normal database operations continue), the headerinformation remains unchanged.

Once the backup of the tablespace is complete, the command ALTERTABLESPACE END BACKUP makes sure that theheader information of the files is updated.

Offline

After an offline backup of the complete database, you have a backup of thedatabase that is consistent. If you work with the database after the backup, thebackup is no longer up-to-date. In this case, you have to recover the databaseafter you restore the backup, using the redo log files.


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Backup types Contd.,

Online_cons- In this backup, the archive logs generated during the backup are also taken


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Backup Types Contd.,

Whole backup

Backs up all database files, but this backup is not cataloged as a level-0 backup, whichmeans that you cannot use it as a reference backup for an incremental backup withRMAN. The syntax for a whole backup is as follows:

- In profile init.sap: backup_mode = all

- With BRBACKUP: brbackup -m all

Full backup

Backs up all database files. You can perform a full backup with or without RMAN. If youdo not use RMAN, then RMAN is called separately to catalog the backup as level 0.This means that you can use this backup as a reference backup for an incrementalbackup with RMAN. The syntax for a full backup is:

- In profile init.sap: backup_mode = full

- With BRBACKUP: brbackup -m full

In the context of the Recovery Manager this backup is an incremental level-0 backup


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Backup types Contd.,

Incremental backupTo be able to make an incremental backup, we must first make a full backup

(level 0). A full backup of the database backs up all Oracle database blocks

that have already been used to store data.

We can then make incremental backups. An incremental backup (level 1,

cumulative) of the database backs up all Oracle database blocks that have

changed since the last full backup (level 0).


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Limitations of Oracle

Maximum number of files per database - DB_FILES- Soft limit

The SAP software value for DB_FILES is 254.

- Hard limit

The hard limit for DB_FILES depends on the operating system but is usually 1022 per

tablespace and 65533 per database.

The Maximum data file size depends Operation System

Minimum Oracle 10.2 patchset is 10.2.0.2

- Oracle 10.2.0.1 is an UNSUPPORTED version

- 10.2.0.3 is not supported in SAP environments

Oracle version 9.2 left Oracle Customer Care support end July 2008- SAP customers who use Oracle 9.2 after 31 July 2010 will be affected regardless

of where they purchased the Oracle license (from SAP or Oracle)

Oracle version 10.1 left Oracle Customer Care support end Jan 2009


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SAPs Oracle support end dates


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Troubleshooting Tips

Alert log file - Oracle's alert.log chronologically records messages and errorsarising from the daily database operation.

- The directory where it is found can be determined by the

background_dump_dest initialization parameter

- The naming convention of the alert log file is alert_.log

DB connectivity

- The db connectivity can be test with SAP program; R3trans (R3trans is used to

transport data between SAP Systems and for the migration between different SAP

releases. )

- To test the connectivity;

R3transx or R3transd (this will logon to the database and check for the connectivity

with SAP and DB)


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References

http://Help.sap.com http://en.wikipedia.org

http://service.sap.com

http://sdn.sap.com/irj/dba
http://help.sap.com/http://en.wikipedia.org/http://service.sap.com/http://sdn.sap.com/irj/dbahttp://sdn.sap.com/irj/dbahttp://service.sap.com/http://en.wikipedia.org/http://help.sap.com/


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Kishore Soma

Engineer

SAP BASIS TeamGSMC

Wipro Ltd (Infotech Div.)

oracle basics

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