Learning of oracle 11g Database for juniors and professionals

What is Automatic Storage Management?
Automatic Storage Management (ASM) is an joined, high-performance database file system and disk manager. ASM is based on the principle that the database should manage storage instead of requiring an administrator to do it. ASM eliminates the need for you to directly manage potentially thousands of Oracle database files.
ASM groups the disks in your storage system into one or more disk groups. You manage a small set of disk groups and ASM automates the placement of the database files within those disk groups.
ASM provides the following benefits:
• Striping—ASM spreads data evenly across all disks in a disk group to improve performance and distribution. This even distribution of database files eliminates the need for regular monitoring and I/O performance tuning.
For example, if there are six disks in a disk group, pieces of each ASM file are written to all six disks. These pieces come in 1 MB chunks known as extents. When a database file is created, it is striped (divided into extents and distributed) across the six disks, and allocated disk space on all six disks grows evenly. When reading the file, file extents are read from all six disks in parallel, greatly increasing performance.
• Mirroring—ASM can increase availability by optionally mirroring any file. ASM mirrors at the file level, unlike operating system mirroring, which mirrors at the disk level. Mirroring means keeping redundant copies, or mirrored copies, of each extent of the file, to help avoid data loss caused by disk failures. The mirrored copy of each file extent is always kept on a different disk from the original copy. If a disk fails, ASM can continue to access affected files by accessing mirrored copies on the surviving disks in the disk group.
ASM supports 2-way mirroring, where each file extent gets one mirrored copy, and 3-way mirroring, where each file extent gets two mirrored copies.
• Online storage reconfiguration and dynamic rebalancing—ASM permits you to add or remove disks from your disk storage system while the database is operating. When you add a disk, ASM automatically redistributes the data so that it is evenly spread across all disks in the disk group, including the new disk. This redistribution is known as rebalancing. It is done in the background and with minimal impact to database performance. When you request to remove a disk, ASM first rebalances by evenly relocating all file extents from the disk being removed to the other disks in the disk group. Fortnite
• Managed file creation and deletion—ASM further reduces administration tasks by enabling files stored in ASM disk groups to be Oracle-managed files. ASM automatically assigns filenames when files are created, and automatically deletes files when they are no longer needed. For information about Oracle-managed files, see Oracle Database Administrator's Guide.
Oracle recommends that you use ASM for your database file storage, instead of raw devices or the operating system file system. However, databases can have a mixture of ASM files and non-ASM files. Oracle Enterprise Manager includes a wizard that enables you to migrate non-ASM database files to ASM.
The ASM Instance
ASM is implemented as a special kind of Oracle instance, with its own System Global Area and background processes. The ASM instance is tightly integrated with the database instance. Every server running one or more database instances that use ASM for storage has an ASM instance. In a Real Application Clusters environment, there is one ASM instance for each node, and the ASM instances communicate with each other on a peer-to-peer basis. Only one ASM instance is required for each node regardless of the number of database instances on the node.
Administering ASM
You administer ASM with Oracle Enterprise Manager Database Control or Grid Control. This Appendix assumes that you are using Database Control.

A short definition of keys in oracle database

Primary Key
Primary key is a set of one or more fields/columns of a table that uniquely identify a record in database table. It cannot accept null, duplicate values. Only one Candidate Key can be Primary Key.

Foreign Key
Foreign Key is a field in database table that is Primary key in another table. It can accept multiple null, duplicate values.

Candidate Key
A Candidate Key is a set of one or more fields/columns that can identify a record uniquely in a table. There can be multiple Candidate Keys in one table. Each Candidate Key can work as Primary Key.
Example: In below diagram ID, RollNo and EnrollNo are Candidate Keys since all these three fields can be work as Primary Key.

Alternate key
A Alternate key is a key that can be work as a primary key. Basically it is a candidate key that currently is not primary key.

Composite/Compound Key
Composite Key is a combination of more than one fields/columns of a table. It can be a Candidate key, Primary key.

Unique Key
Uniquekey is a set of one or more fields/columns of a table that uniquely identify a record in database table. It is like Primary key but it can accept only one null value and it can not have duplicate values.
Super Key
Super key is a set of one or more than one keys that can be used to identify a record uniquely in a table. Example :Primary key, Unique key, Alternate key are subset of Super Keys.

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Learning of oracle 11g Database for juniors and professionals Free learning of oracle database and answering the question regards of oracle 11g database

IF WE WANT TO CREATE OR DELETE A DATABASE IN ORACLE 11G SO FOLLOW THE WAY
DBCA is a utility through which we can create and delete a database as bellow
[ server ]$ cd $ORACLE_HOME/bin
[ server bin] $ dbca

then you graphically can delete and create a database ...

what is oracle database?
Oracle database (Oracle DB) is a relational database management system (RDBMS) from the Oracle Corporation. Originally developed in 1977 by Lawrence Ellison and other developers, Oracle DB is one of the most trusted and widely-used relational database engines.

The Oracle database has its own network component to allow communications across networks.
Oracle DB is also known as Oracle RDBMS and, sometimes, just Oracle.

What is a database?
A database is an organized collection of related data, stored and accessed electronically.