Description of the relationship between maxdatafiles and db_files in the Oracle control file and the maximum datafiles in the database

 

 

1. maxdatafiles parameters in the control file

For instructions on Oracle control files, refer to my previous blog:

Oracle Control File

Http://blog.csdn.net/tianlesoftware/article/details/4974440

 

There is a parameter in the control file of Oracle: maxdatafiles, which is used to control the maximum number of datafiles supported by the database. You can modify this parameter when using dbca to create an instance.

 

You can also view this parameter through the dump control file:

SQL> oradebug setmypid

Statement processed.

SQL> alter Database Backup controlfileto trace;

Database altered.

SQL> oradebug tracefile_name

D: \ app \ Administrator \ diag \ RDBMS \ newccs \ trace \ newccs_ora_6960.trc

 

Trace content:

Create controlfile reuse Database "newccs" resetlogs archivelog

Maxlogfiles 16

Maxlogmembers 3

Maxdatafiles 100

Maxinstances 8

Maxloghistory292

-- 100 is the default value in the control file.

 

 

2. db_files Parameters

Description of this parameter on Oracle 11gr2:

Http://docs.oracle.com/cd/E11882_01/server.112/e25513/initparams057.htm

 

 

Property	Description
Parameter type	Integer
Default Value	200
Modifiable	No
Range of Values	Minimum: the largest among the absolute file numbers of the datafiles in the database Maximum: Operating System-dependent
Basic	No
Oracle RAC	Multiple instances must have the same value.

 

Db_files specifies the maximum numberof database files that can be opened for this database. the maximum valid valueis the maximum number of files, subject to operating system constraint, thatwill ever be specified for the database, including files to be addedby add datafile statements.

The -- db_files parameter specifies the maximum number of datafiles that can be opened by the database. The maximum value is also limited by the operating system.

 

If you increasethe value of db_files, then you must shut down and restart all instancesaccessing the database before the new value can take effect. if you have every mary and standby database, then they shoshould have the same value for thisparameter.

-- If we increase the value of db_files, We must restart the instance to make the modification take effect. In the DG Environment, the parameters of the master and slave databases must be consistent.

 

In Oracle 11gr2, the default value of this parameter is 200, which is greater than the default value of the control file.

 

3. Control the relationship between maxdatafiles and db_files in the file

Mos document: kccrsz: Expanded controlfile message in "alert. log" [ID 101020.1]

 

 

Problem description

-------------------

 

The "alert. log" file shows thefollowing message:

Kccrsz: Expanded controlfile section 4 from 17 to 18 Records

Number of logical blocks in Section remains at 2

Completed: Alter tablespace tb1 add datafile

 

 

Solution description

--------------------

 

Starting inoracle8 the controlfile is automatically expanded. A new datafile is addedbeyond the maxdatafiles limited specified in the control file.

-- The control file is automatically extended from Oracle 8. When the number of newly added datafiles exceeds the control limit of the null maxdatafiles parameter, the value of maxdatafiles will automatically increase.

-- This verification can be viewed through the dump control file.

 

This alsohappens if new records are added to the "log_history" section of thecontrol files and there are no entries that cocould be replaced.

-- Automatic expansion of control files also occurs when the section is insufficient.

 

The routine thatperforms the expansion writes this message to the Alert Log. The messagesspecifies the section that was expanded and the amount of the expansion. pleasenote that this message cannot be turned off.

-- Some log information will be written to the Alert Log when the extension operation is executed, that is, the content above. This part lists the extended sections and the number of extensions, the display information cannot be disabled.

 

The automatic expansion only occurs up to the limit of the "init. ora" parameter "db_files ".

-- Note that the maximum value of the automatic control extended datafile in the control file is the value of our db_files parameter. So this is why we have seen that the value of db_files is greater than the default value in the control file.

 

 

 

Summary:

The maximum number of datafiles in the database is determined by the db_files parameter. Although there are limits in the control file, the limit parameters in the control file are automatically increased until the value of db_files is reached.

 

 

 

 

 

 

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------- Add a group to describe the relationship between Oracle tablespace and data files in the remarks section. Otherwise, reject the application ----

Dba1 group: 62697716 (full); dba2 group: 62697977 (full) dba3 group: 62697850 (full)

Super DBA group: 63306533 (full); dba4 group: 83829929 dba5 group: 142216823

Dba6 group: 158654907 dba7 group: 172855474 DBA group: 104207940