Startup consists of 3 phases.
First of all, in order to issue the startup command you must be logged into an account that has sysdba or sysoper privileges such as the SYS account.
When oracle tries to open a database using startup command it goes through 3 phases.
1.NOMOUNT
2.MOUNT
3.OPEN
1. NOMOUNT Stage:- When we issue the startup command, oracle first enters into nomount stage.In this stage it reads the initialization parameter file(spfile) in $ORACLE_HOME/dbs location.
Lets assume database sid is orcl. So in order to start the orcl instance oracle would first look for spfileorcl.ora . if it cant find the file, then it looks for spfile.ora if not found
initorcl.ora.
After the parameter file is read by oracle, memory areas associated with the database instance are allocated. Also, during the nomount stage, the Oracle background processes are started.
Together, these processes and the associated allocated memory are known as Oracle instance. Now once instance has started its considered to be in nomount stage.
2.MOUNT Stage:-When the startup command steps into mount stage, it first reads the spfile/pfile to know the control file location and read controlfile's content.
From control file's content it gets to know about
a.The database name
b.The location of datafiles and redo logfiles
c.Current log sequence number.
d.Time stamp of database creation.
e.Checkpoint information.
In this stage , oracle confirms the location of the datafiles, but does not open them. Once the datafile locations have been identified, the database is ready to be opened.
3.OPEN Stage :- The last startup step for an Oracle database is the open stage. When Oracle opens the database, it accesses all of the datafiles associated with the database. Once it
has accessed the database datafiles, Oracle makes sure that all of the database datafiles are consistent. Finally users can access the database now.
Reference:- http://www.dba-oracle.com/concepts/starting_database.htm
Reference:-https://docs.oracle.com/cd/B28359_01/server.111/b28310/start001.htm#i1006285
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First of all, in order to issue the startup command you must be logged into an account that has sysdba or sysoper privileges such as the SYS account.
When oracle tries to open a database using startup command it goes through 3 phases.
1.NOMOUNT
2.MOUNT
3.OPEN
1. NOMOUNT Stage:- When we issue the startup command, oracle first enters into nomount stage.In this stage it reads the initialization parameter file(spfile) in $ORACLE_HOME/dbs location.
Lets assume database sid is orcl. So in order to start the orcl instance oracle would first look for spfileorcl.ora . if it cant find the file, then it looks for spfile.ora if not found
initorcl.ora.
After the parameter file is read by oracle, memory areas associated with the database instance are allocated. Also, during the nomount stage, the Oracle background processes are started.
Together, these processes and the associated allocated memory are known as Oracle instance. Now once instance has started its considered to be in nomount stage.
2.MOUNT Stage:-When the startup command steps into mount stage, it first reads the spfile/pfile to know the control file location and read controlfile's content.
From control file's content it gets to know about
a.The database name
b.The location of datafiles and redo logfiles
c.Current log sequence number.
d.Time stamp of database creation.
e.Checkpoint information.
In this stage , oracle confirms the location of the datafiles, but does not open them. Once the datafile locations have been identified, the database is ready to be opened.
3.OPEN Stage :- The last startup step for an Oracle database is the open stage. When Oracle opens the database, it accesses all of the datafiles associated with the database. Once it
has accessed the database datafiles, Oracle makes sure that all of the database datafiles are consistent. Finally users can access the database now.
Reference:- http://www.dba-oracle.com/concepts/starting_database.htm
Reference:-https://docs.oracle.com/cd/B28359_01/server.111/b28310/start001.htm#i1006285
Please share your ideas and opinions about this topic.
If you like this post, then please share with others.
Please subscribe on email for every updates on mail.
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