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Tablespace creation is a snap with Oracle Managed Files

Oracle Tips by Burleson Consulting

September 5, 2002

Oracle9i introduces a new feature that simplifies tablespace creation. This new feature, Oracle Managed Files (OMF), makes life easier for Oracle DBAs by removing the tedium from creating and managing Oracle data files.

Before OMF, Oracle DBAs had to take several manual steps before adding a data file. A simple example of these steps follows, but note that you must know the location of the directory that contains the Oracle data files:

create tablespace
users_02
add
'c:oracleoradatadiogenesusers02.dbf'
size
20m ;

In this example, you must know the following information to create a new tablespace:

The proper file location
The proper filename
The proper file size

Prior to OMF, you needed to execute queries to get the filenames and file locations, interrogating the dba_data_files view to find the appropriate location for a new data file, as shown in Listing A..

Listing A

SQL> select file_name from dba_data_files;
 FILE_NAME

------------------------------------------------
 C:ORACLEORADATADIOGENESSYSTEM01.DBF
 C:ORACLEORADATADIOGENESUNDOTBS01.DBF
 C:ORACLEORADATADIOGENESCWMLITE01.DBF
 C:ORACLEORADATADIOGENESDRSYS01.DBF
 C:ORACLEORADATADIOGENESEXAMPLE01.DBF
 C:ORACLEORADATADIOGENESINDX01.DBF
 C:ORACLEORADATADIOGENESTOOLS01.DBF
 C:ORACLEORADATADIOGENESUSERS01.DBF
 C:ORACLEORADATADIOGENES16K_TS.DBF

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Listing A

SQL> select file_name from dba_data_files;

 FILE_NAME

------------------------------------------------
 C:ORACLEORADATADIOGENESSYSTEM01.DBF
 C:ORACLEORADATADIOGENESUNDOTBS01.DBF
 C:ORACLEORADATADIOGENESCWMLITE01.DBF
 C:ORACLEORADATADIOGENESDRSYS01.DBF
 C:ORACLEORADATADIOGENESEXAMPLE01.DBF
 C:ORACLEORADATADIOGENESINDX01.DBF
 C:ORACLEORADATADIOGENESTOOLS01.DBF
 C:ORACLEORADATADIOGENESUSERS01.DBF
 C:ORACLEORADATADIOGENES16K_TS.DBF

Using the output of the previous query, the C:OracleOradataDiogenes directory is the proper location to add a new Oracle data file.

Viewing tablespace information was also cumbersome. You had to write a query to join dba_tablespaces with dba_data_files to get the file sizes, as shown in Listing B.

Listing B

column file_name  format a40
column tablespace format a15
column bytes      format 999,999,999

select
   file_name,
   t.tablespace_name tablespace,
   bytes
from
   dba_data_files  d,
   dba_tablespaces t
where
   t.tablespace_name = d.tablespace_name ;

The output is shown in Listing C.

Listing C

FILE_NAME                                TABLESPACE             BYTES

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

C:ORACLEORADATADIOGENESSYSTEM01.DBF  SYSTEM           340,787,200

C:ORACLEORADATADIOGENESUNDOTBS01.DBF UNDOTBS          209,715,200

C:ORACLEORADATADIOGENESCWMLITE01.DBF CWMLITE           20,971,520

C:ORACLEORADATADIOGENESDRSYS01.DBF   DRSYS             20,971,520

C:ORACLEORADATADIOGENESEXAMPLE01.DBF EXAMPLE          159,907,840

C:ORACLEORADATADIOGENESINDX01.DBF    INDX              26,214,400

C:ORACLEORADATADIOGENESTOOLS01.DBF   TOOLS             10,485,760

C:ORACLEORADATADIOGENESUSERS01.DBF   USERS             26,214,400

C:ORACLEORADATADIOGENES16K_TS.DBF    TS_16K            10,485,760

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Listing C

FILE_NAME                                TABLESPACE             BYTES

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

C:ORACLEORADATADIOGENESSYSTEM01.DBF  SYSTEM           340,787,200

C:ORACLEORADATADIOGENESUNDOTBS01.DBF UNDOTBS          209,715,200

C:ORACLEORADATADIOGENESCWMLITE01.DBF CWMLITE           20,971,520

C:ORACLEORADATADIOGENESDRSYS01.DBF   DRSYS             20,971,520

C:ORACLEORADATADIOGENESEXAMPLE01.DBF EXAMPLE          159,907,840

C:ORACLEORADATADIOGENESINDX01.DBF    INDX              26,214,400

C:ORACLEORADATADIOGENESTOOLS01.DBF   TOOLS             10,485,760

C:ORACLEORADATADIOGENESUSERS01.DBF   USERS             26,214,400

C:ORACLEORADATADIOGENES16K_TS.DBF    TS_16K            10,485,760

Oracle Corporation recognized that this was a lot of work just to add a data file, so it developed OMF to reduce the complexity involved in specifying all the detailed file information. Some of the benefits of OMF are:

Easier Oracle file management—All files are placed into the proper OS directory.
Easier third-party application integration—Third-party apps don’t have to be aware of OS-specific environments.
Reduction of Oracle file management errors—No risk of human error.
Enforcement of Optimal Flexible Architecture (OFA) standards—OMF will comply with the OFA standards for filename and file locations.
Default file sizes—OMF allows files to have standard, uniform sizes.

File size and naming standards
Before OMF appeared, Oracle DBAs could create data files with any name they chose. While the file suffix was normally .dbf, the Oracle DBA was free to create any type of filename desired. For example, the following is a silly but legitimate Oracle command:

create tablespace
new_ts
datafile
c:windowsProgram Filesautoexec.bat’
size
300m;

As we can see from this example, allowing the developer to choose filenames and locations can have disastrous effects. When using OMF, files typically have a default size of 100 MB and are named using a format mask for the filename.
Listing D presents the format mask that OMF uses when creating new data files.

Listing D

  u% is a unique 8 digit code,
  g% is the logfile group number,
  %t is the tablespace name:
 
Controlfiles        ora_%u.ctl
Redo Log Files      ora_%g_%u.log
Datafiles           ora_%t_%u.dbf
Temporary Datafiles ora_%t_%u.tmp

Listing D

u% is a unique 8 digit code,
 g% is the logfile group number,
 %t is the tablespace name:
 Controlfiles ora_%u.ctl
 Redo Log Files ora_%g_%u.log
 Datafiles ora_%t_%u.dbf
 Temporary Datafiles  ora_%t_%u.tmp

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With OMF, tablespace creation syntax is simplified, and it becomes easy to allocate a new tablespace:

SQL> create tablespace new_ts;
Tablespace created.

Now that the benefits of OMF are apparent, I’ll examine the process for installing and using it. To use OMF, you must set the db_create_file_dest parameter. Once this is set, OMF is installed and tablespace creation becomes super easy:

SQL> alter system set db_create_file_dest=’c:oracleoradatadiogenes;
System altered.
SQL> create tablespace test;
Tablespace created.

Now I’ll look at the filename, directory name, and size for the file that was created as a result of this command in Listing E.

Listing E

FILE_NAME                                          TABLESPACE             BYTES

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

C:ORACLEORADATADIOGENESORA_TEST_YNJ2K200.DBF   TEST             104,857,600

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Listing E

FILE_NAME                                          TABLESPACE             BYTES

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

C:ORACLEORADATADIOGENESORA_TEST_YNJ2K200.DBF   TEST             104,857,600

Listing E shows that OMF created the file as follows:

File location—C:OracleOradataDiogenes
Filename—Ora_test_ynj2k200.dbf
File size—100 MB

Note that the OMF default file size is 100 MB, and the file size can’t be overridden at the command line. You can specify the file size only if you bypass OMF and specify the filename and location in the data file clause.

Oracle enhanced the Oracle9i alert log to display messages about tablespace creation and data file creation. To see the alert log, you must go to the Background_dump_destination directory. You get the location of this directory by issuing the command in Listing F.

Listing F

SQL> show parameter background_dump

NAME                                 TYPE        VALUE

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

background_dump_dest                 string      C:oracleadmindiogenesbdump

Listing F

SQL> show parameter background_dump

NAME                                 TYPE        VALUE

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

background_dump_dest                 string      C:oracleadmindiogenesbdump

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Now that you know the location of the alert log, go to that directory and issue a dir command to see the alert log file, named DiogenesALRT.LOG (Figure A).

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