Explain # CNCPT001oracle database introduction schema in oracledb, schema or schema
Article Source Home/Database/Oracle Database Online Documentation 11g Release 2 (11.2)/Database Administration http://docs.oracle.com/cd/E11882_01/server.112/e40540/intro.htm#CNCPT001 oracle Database introduction schema in oracle db, schema or schema
Article Source
- Home/Database/Oracle Database Online Documentation 11g Release 2 (11.2)/Database Administration
- Http://docs.oracle.com/cd/E11882_01/server.112/e40540/intro.htm#CNCPT001
Oracle Database introduction schema
- In oracle db, the schema or schema object is a set of logical data structures.
- Schema is the data structure created by the user. It has multiple types. The most important of them isTableAndIndex
- A schema object is a type of database object. Many database objects, such as profile or role, are not schema objects.
- Table: Describes entity. The table consists of table names and column sets. The column includes the column name, column data type, and data type length. A table can also be a set of rows; the column specifies the attribute of entity, and the row specifies the instance of entity. In addition, you can set integrity constraints for each column.
- Index: an optional data structure that can be created in one or more columns of a table. Therefore, it is independent from the data (logical or physical), which means that, you can delete an index without affecting applications.
Data access
- SQL
- Query data
- Insert, update, and delete rows
- Create, replace, modify, and delete objects
- Control database and Its Object Access Permissions
- Ensure Database Consistency and integrity
Transaction Management
- Transaction
- Data concurrency
- Use lock mechanism for maintenance
- Data Consistency
- Dirty read: the data that the user is reading is modified by another user but not submitted.
- Read consistency: read consistency
Oracle Architecture
- A database server corresponds to one database and at least one instance.
- Database: a collection of files used to store data, which can exist independently of database instances.
Database instances: A group of memory structures consisting of SGA and background processes. Instances can exist independently relative to database files.
A database can be considered physically or logically.
- The data in the physical structure is visible to the operating system.
- The logical structure only makes sense to the database
Database Storage Structure
- Physical storage structure
- Data Files
- Control File
- Online redo log files
- Other files
- Logical Storage Structure
- Data Block (data blocks vs OS block)
- Zone (extents)
- Segment (segments)
- Table space)
- Database instance
- Process: a mechanism that can run a series of steps on the Operating System
- Client process: Used to run application code or oracle tools
- Background processes: these processes are used to run various programs, asynchronously use IO, and monitor database processes to prevent increasing concurrency, thereby improving performance and reliability.
- Server process: interacts with the customer process and the database to allow the database to complete client process requests.
- Note: oracle processes include server processes and background processes. In most environments, oracle and client processes run on different machines.
- Memory Structure of the Instance
- System Global Area (SGA): A group of shared memory structures that contain the control information of a database instance.
- Program Global Areas (PGA): A memory zone with control information of the server or background process. For processes, access to pga is exclusive, and each server process and background process has their own pga
Application and Network Structure
- Application Structure
- Network Structure
- Oracle Net Services: interfaces for database and network communication protocols; network communication protocols are conducive to distributed processing and distributed databases; Communication Protocols define methods for data transfer and receipt over the network. Oracle net services supports all major network protocols, including TCP/IP, HTTP, FTP, and WebDAV.
- Oracle Net: A Component of Oracle Net Services. It establishes and maintains network sessions between client programs and database servers. When a session is established, it acts as a data courier and exchanges information between the client program and the database server. It exists on each computer in the network.
- Oracle Net Listener (called the listener): is an independent process that runs on a database server or elsewhere in the network. the client program can send a connection request to the Listener, let it process these requests for the database server. When a connection is established, the client and the database can communicate directly.
- In most cases, the methods for configuring Database Service requests for the client are as follows:
- Dedicated server architecture (Dedicated server architecture): each client process is connected to a Dedicated server process, which is not shared. Each new session is assigned a Dedicated server process.
- Shared server architecture (Shared server architecture): the database uses a Shared process pool to serve multiple sessions. The client process communicates with the scheduler.
