Oracle

Oracle databases are able to support multiple users, 100's of users can use the database concurrently. The database is very reliable and has excellent backup and recovery features. Millions of records can be exported or imported easily. As the database uses a feature called Time Stamping records are not locked for longer than required when updates are made to the database. The database can be installed on various platforms such as NT, Unix, VMS etc. Oracle can be installed as a stand alone 'lite version' or as client server architect and can be tailored to individual business requirements. 

Creating a New Oracle Database

    Database Planning 

When creating a new database, you should consider the size of the data files, data blocks, tables and indexes. 
You should also plan for the location of control files, at least two control files should be created and stored on different disks. This ensures that if a control file or a disk that stores a control file is corrupted, then the other control file can be accessed by the database. One should also consider the character set to be used for the database. After a database is created, the specified character set cannot be changed unless the database is recreated. 

Another guideline for planning the physical database design is that online redo log files of a database should 
consist of multiplexed groups of online redo log files. A redo log group consists of identical copies of redo log 
files. Members of a redo log group should also be stored on separate disks. This ensures that a disk failure does not cause the LGWR and the database instance to fail. 

The next guideline for planning the physical database design is that the data files that contain database objects 
with different life spans, such as application data and temporary data, should be separated. This helps to 
minimize database fragmentation.

    Creating the database

When Oracle is installed on a system, it automatically creates an initial database. This initial database may not suit your business requirements, if so please follow the steps bellow.

Once all the files are installed from the Oracle CD one needs to edit the Init.ora file, Modify the windows registry for Oracle and  create the database using the create database command on server manager. Before any database is created one needs to decide on a unique instance and a database name.

    Parameters to change on the init.ora file.

Using the operating system copy the parameter file and give this parameter file a new name. next edit the following parameters in the new init.ora file and save.

 

 

    Parameters to change on the Registry file.

Specify the home directory path in the Windows NT registry where the Oracle software is installed. This is 
specified in the ORACLE_HOME registry variable. For example if the oracle software is installed in C:\orant directory set the variable of  Oracle_home to  C:\orant

Set the ORACLE_ SID to the default instance name ie orac1

Set the search path in the path Variable.

Next et the character path if the default character set is not used in the  ORA_NLS33 registry variable.

    The next stage is to create the actual database  

 

Reasons why the create database command fails may be because

  1. syntax error on the script.
  2. insufficientdisk space.
  3. Files created by the command already exist.

When you create a database, Oracle creates the following objects.

  1. System Table space.

  2. Data Dictionary Tables.

  3. Control files.

  4. Redo Logfiles.

  5. Users sys and System with passwords change_on_install and Manager.
  6. System roll back segment -- to record changes made to the system table space.

    Creating table spaces

Next all the table spaces, rollback segments, and users need to be created.

The next thing to do is to create the tables, indexes, triggers, and procedures.

Once all this is done one needs to enter the data into the tables. The imp feature can be used to import the data into the database.