Basic Concepts of Oracle Database

First, the database
When we install the Oracle database, the global database name: is the identity of a database, in the installation must think well, later generally do not modify, modification is also troublesome, because once the database is installed, the database name is written into the control files, database tables, many places will use the database name.

Start the database: Also called the global database, is the entry of the database system, it will be built with some advanced permissions of users such as Sys,system. With these advanced rights accounts, we can create table spaces, users, and tables in a DB instance.

　

Second, the database instance

　　With Oracle official description: An instance is a subset of the computer memory and secondary processing background processes required to access an Oracle database, which is a collection of processes and the memory (SGA) used by those processes.

It is actually a piece of process used to access and use the database, it only exists in memory. Just like the new instance object in Java.

We visit Oracle to access an instance, but if the instance is associated with a database file, it can be accessed, and if not, you will get an error that the instance is not available.

The instance name refers to the name of the database management system that is used in response to a database operation. She is also called SID. The instance name is determined by the parameter instance_name.

The database instance name (instance_name) is used for external connections. To get a connection to the database in the operating system, you must use the database instance name. For example, to connect to a database, we have to connect to the database instance name:

　　a database can have multiple instances , which can be used when serving as a database service cluster.

Three, table space

　　An Oracle database is a table space for storing physical tables, a database instance can have n table spaces, and a table space can have n tables.

With the database, you can create table spaces. A tablespace is a concept used to manage the logic of data storage, where a tablespace is simply related to a data file (ora or dbf file), the data file is physical, a tablespace can contain multiple data files, and a data file can only be subordinate to one table space.

It contains data files: data Files (dbf, ora):
The data file is the physical storage unit for the database. The data in the database is stored in a table space and is really in one or more data files. A table space can consist of one or more data files, and a data file can belong to only one table space. Once a data file is added to a table space, it cannot be deleted, and if you want to delete a data file, you can only delete the table space it belongs to.

Note: The data in the table is a table space where the user is placed, and the table space randomly places the table data in one or more data files.

　　　

Iv. User

　　After the Oracle database is built, to build the table in the database, you must first establish the user for the database and specify the table space for the user.

The user is created under an instance. Different instances can be built with the same name of the user.

V. Table

　　With a database, table space, and users, you can create tables in your own tablespace with a custom user.

Because Oracle's database is not a common concept, Oracle has users and table spaces to manage and store data. But the table is not a table space to query, but by the user to check. Because different users can create a table of the same name in the same table space! Here the distinction is user!

It is necessary to understand that the physical structure of a database is determined by the operating system files of the database, and that each Oracle database consists of three types of files: Data files, log files, and control files. The database's files provide true physical storage for database information.

Each Oracle database has one or more physical data files. A database data file contains all of the database data. The data for a logical database structure (such as tables, indexes, and so on) is physically stored in the data file of the database. The data file is usually in *.dbf format, for example: USERCIMS.DBF. Data files have the following characteristics: ①, a data file is only associated with one database; ②, once established, data files only increase; ③, a tablespace (a logical unit of database storage) consists of one or more data files.

Transfer from http://blog.csdn.net/z69183787/article/details/23526423 http://www.cnblogs.com/adforce/p/3312252.html

Basic Concepts of Oracle Database (RPM)