Remote DBA team- Oracle Database Startup & Shutdown Process

DBAMETRIX Solutions Present Oracle Startup & Shutdown Process

Oracle DBA Learn by Presentation series • Oracle DBA learning by presentation offered by DBAMETRIX Solutions. • This all presentations have been prepared by Gitesh P Trivedi. • Gitesh Trivedi has 14 years working experience in DBA field and as expert consultant faculty. • For discussing and solving problem please log in http://dbametrix.wordpress.com/ • For more details please contact to www.dbametrix.com or gitesh@dbametrix.com or giteshtrivedi@yahoo.com

In this session we get detail information for following topics • Which type of shutdown options available • Which type of startup options available • How Oracle database shutdown • How SGA de-allocates from memory region • How Oracle protects committed and un-committed data • How Oracle performs normal startup • How Oracle checks datafiles and controlfiles using internal check-up • How Oracle enables & performs recovery process • What are the internal processes

Shutdown Process • Following options are available in Oracle • Shutdown normal • Shutdown transactional • Shutdown immediate • Shutdown abort

Shutdown normal • Using command “shutdown;” or “shutdown normal;”. • Default option is normal. • Oracle triggers checkpoint process and all dirty buffers flush in to disk. • Checkpoint writes stop system change number (STOP SCN) in to controlfile and updates all respective datafile header. • Oracle drops all temporary segments from temp tablespaces. • Oracle closes all datafiles and online redologfiles. • Oracle de-allocates SGA from memory region of operating system.

Shutdown Normal New connection not Existing Session can allow do work Buffer Log Buff Shared Pool C Cache er on St r Sort Ext Pool SGA Control File Stop: SCN Dbwr Log Writer SCN: Datafiles Log Log File File Group- Group 1 -2

While executing Shutdown Normal • Existing session can perform work. Once those logout after that don’t get connection. • No new session allows. • After all sessions logout then Oracle starts shutdown process. • Checkpoint occurs, dirty buffers flush in to disk. • LGWR flushes data from Log Buffer to Online redo log files. • Stop system change number generates and stores in controlfile (Stop: SCN) as well as all datafiles (Current: SCN). • If shutdown event trigger exists then fires. • Temporary segments drop from temporary tablespace. • Oracle closes all datafiles, redo logs and controlfiles. • Oracle de-allocates shared global area from memory region of Operating system.

Practically we take example of “shutdown” normal command as follows.

Shutdown Transactional New connection not Existing Session can do allow work, End of transaction session ended Buffer Log Buff Shared Pool C Cache er on St r Sort Ext Pool SGA Control File Stop: SCN Dbwr Log Writer SCN: Datafiles Log Log File File Group- Group 1 -2

While executing Shutdown Transactional • Existing session can perform work. Once transaction to be ended it becomes kicked off from database. If logout then also doesn’t get connection. • No new session allows. • After all sessions logout then Oracle starts shutdown process. • Checkpoint occurs, dirty buffers flush in to disk. • LGWR flushes data from Log Buffer to Online redo log files. • Stop system change number generates and stores in controlfile (Stop: SCN) as well as all datafiles (Current: SCN). • If shutdown event trigger exists then fires. • Temporary segments drop from temporary tablespace. • Oracle closes all datafiles, redo logs and controlfiles. • Oracle de-allocates shared global area from memory region of Operating system.

Practically we can take example of “shutdown transactional” as follows

Shutdown Immediate New connection not allow ALL Existing Session disconnect immediately Buffer Log Buff Shared Pool C Cache er on St r Sort Ext Pool SGA Control File Stop: SCN Log Writer Dbwr SCN: Datafiles Log Log File File Group- Group 1 -2

While executing Shutdown Immediate • Existing ALL sessions are kicked off from database. They loose connection from database. • No new session allows. • User will lose all uncommitted transaction data. Immediately Oracle starts shutdown process. • Checkpoint occurs, dirty buffers flush in to disk. • LGWR flushes data from Log Buffer to Online redo log files. • Stop system change number generates and stores in controlfile (Stop: SCN) as well as all datafiles (Current: SCN). • If shutdown event trigger exists then fires. • Temporary segments drop from temporary tablespace. • Oracle closes all datafiles, redo logs and controlfiles. • Oracle de-allocates shared global area from memory region of Operating system.

Practically we can take example of “shutdown immediate” as follows

Shutdown abort New connection not allow ALL Existing Session disconnect immediately Buffer Log Buff Shared Pool C Cache er on St r Sort Ext Pool SGA Control File Stop: SCN Log Writer Dbwr SCN: Datafiles Log Log File File Group- Group 1 -2 Shutdown SGA/Instance

While executing Shutdown ABORT • Existing ALL sessions are kicked off from database. They loose connection from database. • No new session allows. • User will lose all uncommitted transaction data. Immediately Oracle starts shutdown process. • NO Checkpoint occurs & NO dirty buffers flush in to disk. • NO LGWR flushes data from Log Buffer to Online redo log files. • There is no STOP SCN generated and not Controlfile, datafile header updated. • No shutdown event trigger even if exists. • No Temporary segments drop from temporary tablespace. • Oracle closes only Instance (SGA and background processes). • Database will be in inconsistence mode.

Problem occurs during shutdown process • Oracle updates alert.log in every shutdown options. • If any error occurs Oracle logs in to alert.log. • During “shutdown immediate” option, Oracle may takes time for shutting down database due to rollback pending transaction. • Without “abort” option, Database is consistence mode in all other shutting down options. We can take cold backup. • In “shutdown abort” option, database is in inconsistence mode, we can’t take cold backup.

Practically we can take example of “shutdown abort” as follows

Physical structure of Oracle database • Parameter file (init.ora & spfile) • Password file • Control files • Online redo log files • Datafiles • Trace files including alert.log • If sys user’s audit enables then audit files

Startup Process • Step by step startup command • Startup nomount ( only instance started) • Startup mount (control file open and check) • Startup open ( datafiles and redo log files open and check) • Startup force ( forcibly instance start and instance recovery perform) • All commands are available after each step • Oracle logs all details and error in alert.log file during startup command execution

Startup nomount • Oracle reads parameter file and populates instance. • Before startup instance Oracle also checks password file and match it. • Oracle also reads location and name of controlfile from parameter file (init.ora or spfile). • Shared Global Area and background processes are starting. • After finishing command execution successfully, Oracle prompts message “instance started”. • This command is useful for new database creation and controlfile recreation.

Startup nomount Parameter file Buffer Log Buff Shared Pool C Cache er on St r Sort Ext Pool SGA Pmon Dbwr Smon

Startup mount • After instance starts next step is mount. • In mount stage Oracle opens all controlfiles from each location and read contains. It also checks STOP SCN from controlfile. • If controlfile is missing or corrupt, Oracle gives error in mount stage only. • If any datafile or online redo log file is missing there is no error will be generated. • If we started instance using “startup nomount” then we can mount database using “alter database mount;” command.

Startup mount Parameter file Buffer Log Buff Shared Pool C Cache er on St Control r File Sort Ext Pool SGA Pmon Stop: SCN Dbwr Smon

Practically we can take example of “startup” step by step as follows

Startup open • After mounting database, Oracle opens all datafiles and online redo log files. • Oracle matches STOP SCN of controlfile to each and every datafile (from header of datafile). • If Oracle finds any mismatch of this number due to instance crash or “shutdown abort” then it performs instance recovery. • If Oracle finds any mismatch of this number due to not above circumstances then asks for media recovery. • Alternate we can use “alter database open” command after mounting database with “startup mount;”. • If startup event trigger exists then fires after open database.

Startup open Parameter file Buffer Log Buff Shared Pool C Cache er on St Control r File Sort Ext Pool SGA Pmon Stop: SCN Dbwr Smon SCN: Datafiles Log Log File File Group- Group 1 -2

Practically we can take example of normal “startup” as follows

When Oracle performs recovery? • When Instance crashed. • When issued “shutdown abort”. • When mismatch found of SCN of controlfile and any of datafile’s header. • During instance recovery Oracle performs roll-forward and roll-backward scenario. • If Oracle finds any of new datafile or older datafile means new Stop: SCN or older Stop: SCN then asks for media recovery. • After starting database Stop SCN becomes infinitive in controlfile.

DBAMETRIX Solutions Present Oracle Startup and Shutdown Process Prepared By: Gitesh P Trivedi gitesh@dbametrix.com http://www.dbametrix.com

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Remote DBA team- Oracle Database Startup & Shutdown Process Presentation Transcript