Scenario

By default, a database supports a certain number of connections. Administrators can manage database connections to learn about the connection performance of the current database or increase the connection limit so that more users or applications can connect to the database at the same time.

Maximum Number of Connections

The number of connections supported by a cluster depends on its node flavor.

**Table 1** Number of supported connections
Parameter	Node Flavor	Number of CN Connections	Number of DN Connections
max_connections	vCPUs < 16	512	Number of CN connections x 2
	vCPUs > 16 && <= 32	1024	Number of CN connections x 2
	other	2048	Number of CN connections x 2

The policies of comm_max_stream, poolsize, and max_prepared_transactions are the same as those of max_connections.

Viewing the Maximum Number of Connections

Use the SQL client tool to connect to the database in a cluster.
Run the following command:
1
SHOW max_connections;
Information similar to the following is displayed, showing that the maximum number of database connections is 200 by default.
```
max_connections
----------------- 
200
(1 row)
```

Viewing the Number of Used Connections

Use the SQL client tool to connect to the database in a cluster.

View the number of connections in scenarios described in Table 2.

Table 2 Viewing the number of connections

Description

Command

View the maximum number of sessions connected to a specific user.

Run the following command to view the maximum number of sessions connected to user dbadmin.

SELECT ROLNAME,ROLCONNLIMIT FROM PG_ROLES WHERE ROLNAME='dbadmin';

Information similar to the following is displayed. -1 indicates that the number of sessions connected to user dbadmin is not limited.

 rolname  | rolconnlimit
----------+--------------
 dwsadmin |           -1
(1 row)

View the number of session connections that have been used by a user.

Run the following command to view the number of session connections that have been used by dbadmin.

SELECT COUNT(*) FROM V$SESSION WHERE USERNAME='dbadmin';

Information similar to the following is displayed. 1 indicates the number of session connections used by user dbadmin.

 count
-------
     1
(1 row)

View the maximum number of sessions connected to a specific database.

Run the following command to view the upper limit of connections used by gaussdb.

SELECT DATNAME,DATCONNLIMIT FROM PG_DATABASE WHERE DATNAME='gaussdb';

Information similar to the following is displayed. -1 indicates that the number of sessions connected to database gaussdb is not limited.

 datname  | datconnlimit
----------+--------------
 gaussdb |           -1
(1 row)

View the number of session connections that have been used by a database.

Run the following command to view the number of session connections that have been used by gaussdb.

SELECT COUNT(*) FROM PG_STAT_ACTIVITY WHERE DATNAME='gaussdb';

Information similar to the following is displayed. 1 indicates the number of session connections used by database gaussdb.

 count 
-------
     1
(1 row)

View the number of session connections that have been used by all users.

Run the following command to view the number of session connections that have been used by all users:

SELECT COUNT(*) FROM V$SESSION;

Information similar to the following is displayed.

 count
-------
     10
(1 row)

Managing Database Connections

Scenario

Maximum Number of Connections

Viewing the Maximum Number of Connections

Viewing the Number of Used Connections