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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Oracle Architecture Contd.,
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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Oracle Architecture Contd.,
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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Oracle Architecture Contd.,
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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Oracle Architecture Contd.,
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 Architecture Contd.,
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
Oracle Architecture Contd.,
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Oracle Architecture Contd.,
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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Oracle Architecture Contd.,
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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Oracle Architecture Contd.,
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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Oracle Architecture Contd.,
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
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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.)
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