Oracle series: getting started with Oracle

Oracle series: getting started with Oracle

1. What is Oracle?
1. Oracle is an object relational database management system (ordbms );
2. Based on the Client/Server (C/S) system structure, it is an interface between the user and the database.
The client interacts with the user, and the server executes database operations.

Ii. What are the features of Oracle?
1. Large Databases for enterprise applications;
2. high security and integrity;
3. Distributed Processing;
4. Portability;
 
Iii. What is the Oracle architecture and composition of the Oracle server?

1,Oracle ServerIt is composed of Oracle databases and Oracle instances. Each running Oracle database is associated with an oracle instance.

2. What are Oracle databases and Oracle instances? What is the relationship between them?
① Oracle database is a data set. A series of processes are required for management, while processes need to use memory. The collection of background processes and memory structures (SGA) is called an oracle instance.
② An instance can only open and use one database.

3. What is the structure of the Oracle database? 
① Physical structure: a group of operating system files (database files) in the database -- (Knowledge Association: tablespace ).
② Logical structure: the logical relationship formed after the database is created.
 
4. What is the structure of Oracle instances?
① System global zone (SGA );
② Background process;

5. What is a session?
①. A single connection between the user and the Oracle server.
② Parallel sessions: when a user connects to the server using multiple different applications or terminals at the same time, multiple parallel sessions are created for the user.

6. What is the memory structure of Oracle?
① System global zone (SGA): A group of shared memory structures that contain data and control information of an Oracle instance. Stores database information and is shared by multiple database processes. Is an important indicator that affects database performance.
√ Memory Structure
Shared Pool: the memory area in which SQL pl/SQL programs are operated;
Database Buffer: used to store data read from disk data files;
Log Buffer: records all changes to the database for data recovery.
② Program global zone (PGA ):
Contains the data and control information required by a single server process. Automatically assigned when a session is created. A non-shared zone is used by a single process. The PGA is released when the session ends.
 
7. What is an oracle process?
① User process: the program that creates the process when interacting with the server.
② Service process: Process requests from user processes connected to the instance.
③ Background process: Processes attached to the instance system exist in the operating system.
 
4. Oracle physical components
Oracle physical components refer to the operating system physical files used after the Oracle database is created.
Data File: The file that stores the database data.
Log File: records database operation information.
Control File: a binary file that records the physical structure of the database. Each Oracle database contains a control file.
 
V. Oracle logical components 

1. What is a tablespace )?
①. The logical components are combined and composed of one or more data files.
② An Oracle database must contain at least one tablespace.
A tablespace contains one or more segments. A segment consists of multiple zones. A zone consists of multiple data blocks.
③ System tablespace: system. Each database has only one.
 
2. What is segment?
A specified type of logical storage structure. There are four types of data segments, index segments, rollback segments, and temporary segments based on data features and optimized performance.
 
3. What is a zone?
The minimum unit for disk space allocation. Segments are allocated space, which consists of continuous data blocks. It cannot exist across data files, but only in one data file.
 
4. What is a data block?
Minimum Data Organization and Management Unit in the database. Data is stored in data blocks and is the smallest unit of storage. The Oracle server manages the storage space of data files in blocks.

5. What is the mode?
All database objects created by the user are collectively referred. A user is associated with a mode with the same name.

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