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This article introduces the relevant knowledge of "what is the process of establishing a connection between Oracle's PGA and database". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

(1) composition and structure of PGA

PGA mainly consists of the following three parts:

Private SQL zone (Private SQL Area): the private SQL zone contains data such as the value of the bound variable and runtime memory structure information.

Cursor and SQL area (Cursors and SQL Areas): provides the necessary resources and space memory for opening cursors and executing SQL

Session memory (Session Memory): session memory is a piece of memory used to hold session variables (such as login information) and other pre-session related information. For shared server mode, session memory is shared, not private.

(2) PGA-related data dictionary

V$PGASTAT: stores some information about pga usage and automatically collects practical information about pga after the instance is started.

V$PGA_TARGET_ADVICE: this view shows the estimated predictions of the PGA optimization advisor, showing the PGA performance statistics that V$PGASTAT might display at various PGA_AGGREGATE_ target values.

(3) the process of PGA and connection establishment

This is shown in the following figure. The client first obtains the IP, port number, usage protocol, service name and other information of the database server from the tnsnames.ora file, and then connects to the database listener to judge whether the service name requested by the user is valid. If it is valid, the client requests the server background process to create a server process and assign it PGA, and then the listener sends the port number and address of the created server program to the user process. The user process is then disconnected from the monitor. The user process can connect to the server process according to the information, and the server process authenticates the user process, usually by entering the account password, and the server process matches the account password with the contents of the data dictionary of the buffer. If the match is successful, the session is established.

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