Shulou(Shulou.com)05/31 Report--

Today, I will talk to you about the difference between exclusive, startup nomount and mountopen, which may not be well understood by many people. In order to make you understand better, the editor has summarized the following contents for you. I hope you can get something according to this article.

Look at the introduction to oracle, which says that starting routines using the startup nomount command cannot be used with mount open and exclusive. This command can be used when setting up or maintaining a database.

So I checked why they can't be used at the same time, and the difference between them.

The following is a reprint:

Nomount: read the initialization parameter file and start the instance.

Mount: opening control file

Open: open data files, log files

To put it simply, nomount is the state used to create the database, in which case create database.... can be executed

Mount is used to maintain the database, for example, if there is a problem with the database and the data file is deleted by mistake, it cannot be open. At this time, the data file can be removed from the database in the mount state.

Open is a database that can provide services to all users.

Detailed introduction:

1 、 startup nomount

Non-installation startup, which can be executed in this way: rebuild control file, rebuild database

Read the init.ora file and start instance, that is, start the SGA and background processes, which only requires the init.ora file.

2 、 startup mount dbname

Installation startup, which can be executed in this way:

Database log archiving,

Database media recovery,

Bring data files online or offline

Relocate the data file and redo the log file.

Execute "nomount", then open the control file and confirm the location of the data file and the online log file

However, the data file and log file are not checked at this time.

3 、 startup open dbname

Execute "nomount", then "mount", and then open all database files, including Redo log files

The data in the database can be accessed in this way.

4. Startup is equal to the following three commands

Startup nomount

Alter database mount

Alter database open

The three steps of database startup the purpose of nomount,mount,open is to understand the three steps to refine the startup database

The conditions for starting the database to the nomount state are as follows. If you are non-windows OS, there is no registry, and OracleService in the environment variable service must be started

The service name matches the oracle_sid in the registry

There are correct password files and parameter files

Have enough memory

The path described in the parameter file must exist

The database product is installed correctly

Conn sys/oracle as sysdba

Shtudown abort

Startup nomount

Select instance_name,status from v$instance

Start the database to the first step nomount state and do the following

1. Read the parameter file

two。 Allocate memory

3. Start the background process

4. Initialize part of the v$ view

Bring the database to the mount state

Select value from v$spparameter where name='control_files'

Alter database mount

The process of mount database is to read the control file described in the parameter file, verify the correctness of the control file, and read the contents of the control file into memory. Mounu means hanging and is a concept in the operating system. Once mount is done, a meaningless instance is associated with a database. Because the instance is an empty shell. There is no relationship between any database and the instance, we can understand that the instance is a water pump, where the data will be extracted from the reservoir, the example is universal. Mount means to put a general-purpose pump into a designated reservoir. Mount is a read control file, which contains information about data files and log files.

Select instance_name,status from v$instance

Open the database

Alter database open

Read the data file described in the control file

Verify the consistency of the files and, if inconsistent, use log files to restore the database files to a consistent state.

After the database open, ordinary users can access the database.

Only the user's table is visible.

Read-only open database

Startup mount

Alter database open read only

Select open_mode from v$database

The default open mode is read write

If you want to change read only to read write, you must restart the database

We now think back to the three steps of database startup. We first read the parameter file, which can be written by us. After reading the parameter file and then read the control file, the control file describes the data file and log file information, if the control file is lost, we can re-establish, and finally read the data file. Our data is stored in the data file. The database will be started up into three steps, so that we can know exactly where there is a problem and eliminate it quickly. It's kind of like an old mopper, with a big head in the back. From the beginning of a 1K parameter file, and finally to several T large databases. When we only type startup without any parameters, the default is to open, which is equal to startup open

We can see clearly from the results on the screen that there are three steps.

Another command is startup force to force the database to start, which is equivalent to forcing the database to stop and then start the database.

After reading the above, do you have any further understanding of the difference between exclusive, startup nomount and mountopen? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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