How to query the number of connections in Oracle database

Oracle is a popular relational database management system whose task is to store and manage large amounts of data. Querying the number of connections becomes particularly important when multiple users are connected to the same database at the same time. Because too many connections may cause database performance degradation or crash. This article will introduce you how to query the number of connections in the Oracle database.

To view the current number of connections, you can use the following command:

SELECT COUNT(*) FROM v$session;

v$session is one of Oracle's views, used to view the session information of all current connections. Use the COUNT(*) function to count the number of rows, that is, the number of connections. This command will return a number representing the number of users currently connected to the database. However, this number may be less than the actual number of connections. Because sometimes after users connect to the database, they do not perform any operations immediately, but wait. At this time, their status is marked as "Inactive", and these inactive connections are not included in the connection count. Therefore, if you wish to get more complete information, use the following command:

SELECT COUNT(*) FROM v$session WHERE STATUS='ACTIVE';

The above command introduces a WHERE clause that limits the query to only active connections. This will give you a more accurate idea of ​​how many users are currently connected to the database.

In addition to viewing the number of connections, you can also use the following command to view the details of each connection:

SELECT sid, serial#, username, machine, status FROM v$session;

This command displays the SID (session identifier), serial number, user of each connection name, host machine and status. If you only want to view the details of active connections, use:

SELECT sid, serial#, username, machine, status FROM v$session WHERE STATUS='ACTIVE';

This command will only display the details of active connections, allowing you to examine the status of each connection more carefully.

If you want to know which processes are occupying database resources, you can use the following command to view the currently running SQL statements:

SELECT sid, serial#, username, machine, status, sql_id, sql_child_number, sql_text FROM v$session WHERE STATUS='ACTIVE' AND username IS NOT NULL;

The above command lists the details of active connections and displays The SQL statement executed by this connection. The SQL statement is represented by its SQL ID, SQL subnumber, and SQL text. This command can help you track which SQL statements are running and check if they are causing performance issues.

In addition, there are other Oracle views and commands to view connection and session information. For example, you can use the following command to view all processes in the current database:

SELECT * FROM v$process;

The above command displays detailed information about all processes in the current database, including process ID, PID, name, type, status, etc. This can help you understand the overall situation of the database system and how many processes are connecting to the database instance.

In general, there are many ways to query the number of connections in the Oracle database, and you can get more detailed information using different commands and views. If you need a deeper understanding of database connections and session management, please refer to Oracle's official documentation, or consult professional Oracle technicians.

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