Three phases of Oracle Startup Mode

Oracle startup is a very basic operation. The following describes the various stages of Oracle Startup Mode in detail. I hope you can learn more about Oracle startup mode.

When the startup command is issued, Oracle starts to start. If the startup is successful, the process of this Oracle startup mode is divided into three stages.

1. nomount stage in Oracle Startup Mode

Nomount: In this startup phase, the main thing Oracle does is to find the relevant startup parameter file and open the startup parameter file according to the parameter values recorded in the startup parameters.

When the instance is started successfully, open the file alert _. ora in the alert file. This file is under ORACLE_BASE/admin/SID/bdump by default and records the relevant startup information. If pfile = ''is specified in startup, Oracle uses the file you specified as the startup parameter file. If pfile is not specified, oracle will first find spfileSID in the default directory ($ ORACLE_HOME. ora. If no spfile is found, search for spfile. ora. If not, find initSID. ora, which is the previous static parameter file. If not, find init. ora; if it is not found, it will be started at this time. The parameter file cannot be found, and the Instance name will be dynamically registered to the listening service.

Of course, before using startup pfile = '', we need to first use create pfile from spfile; the dynamic parameter file of the instance is first export into a static text parameter file, then modify the file according to the appropriate parameters and modify the pfile to start the file.

2. mount phase of Oracle Startup Mode

When the nomount stage is reached, the database can only be started Step by step. Its next start stage is mount. We use alter database mount; to reach the nomount stage or startup mount stage. At this stage, Oracle finds the path parameter value of the control file from the startup parameter file, find all the control files, open the read control file information, and record the information of various tablespace files, log files, and database character sets, in fact, it is the records in the control file (the control file can be specified multiple records, as long as one cannot be read successfully, this phase will fail, the database has read the relevant system file information and character set information, but only reads the system files, which are not actually loaded into the database.

When someone started mount, there was a problem. The last point was that the control file was deleted. The solution was to use the backup control file, then you can recover it. If no backup is available, create a controlfile under nomount.

3. open stage of Oracle Startup Mode

After the mount stage ends, all the information of the database system has been fully read. We know the redo file and data file information, but it has not been loaded yet and is in the open state, the database reads all files. If one file cannot be read successfully, the open stage will fail. At this time, we can solve the problem through the error prompt, data recovery, or error troubleshooting.

Errors in this phase are the most common cause. The processing method is much more complex than the previous one. However, they are basically inconsistent with data files, log files are missing, and data scn, and so on. What we need to do at this time is to recover the data according to the error prompt, and troubleshoot the data. This is the most interesting part of database recovery.
 

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