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DBA - Process: Server Process

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• DBA - Process: Server Process
  • Server Processes
    • Dedicated Server Processes
    • Shared Server Processes
  • How Oracle Database Creates Server Processes

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Server Processes

• Server processes
  • process created by Oracle Database to to handle the requests of client processes connected to the instance.

• A client process always communicates with a database through a separate server process.

• Server processes created on behalf of a database application can perform one or more of the following tasks:
  • Parse and run SQL statements issued through the application, including creating and executing the query plan
  • Execute PL/SQL code
  • Read data blocks from data files into the database buffer cache (the DBW background process has the task of writing modified blocks back to disk)
  • Return results in such a way that the application can process the information

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Dedicated Server Processes

• In dedicated server connections, the client connection is associated with one and only one server process.一对一专用
  • server process is dedicated to its client process for the duration of the session.
  • Each client process communicates directly with its server process.
• The server process stores process-specific information and the UGA in its PGA.内存位置: PGA

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Shared Server Processes

• In shared server connections, client applications connect over a network to a dispatcher process, not a server process.

  • e.g., 20 client processes can connect to a single dispatcher process.

• dispatcher process:

  • receives requests from connected clients and puts them into a request queue in the large pool.

• Request processing: 请求队->shared 服务器进程->回应对->传输

  • The first available shared server process takes the request from the queue and processes it.
  • Afterward, the shared server places the result into the dispatcher response queue.
  • The dispatcher process monitors this queue and transmits the result to the client.

• Memory:

  • a shared server process has its own PGA.
  • The UGA for a session is in the SGA so that any shared server can access session data.

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Mode	Process	Process Location	Session/UGA Location
Dedicated	server process	PGA	PGA
Shared	shared server process	PGA	SGA

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How Oracle Database Creates Server Processes

• The database creates server processes in various ways, depending on the connection methods.

  • Bequeath:
    • SQL*Plus, an OCI client, or another client application directly spawns the server process.
  • Oracle Net listener
    • The client application connects to the database through a listener. 通过监听器
  • Dedicated broker
    • database process that creates foreground processes.
    • the broker resides within the database instance.
    • When using a dedicated broker, the client connects to the listener, which then hands off the connection to the dedicated broker.

• When a connection does not use bequeath, the database creates the server process as follows:

  • 1. The client application requests a new connection from the listener or broker.
  • 1. The listener or broker initiates the creation of a new process or thread.
  • 1. The operating system creates the new process or thread.
  • 1. Oracle Database initializes various components and notifications.
  • 1. The database hands over the connection and connection-specific code.

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