PostgreSQL is a powerful relational database management system that is designed to handle complex data manipulation and retrieval tasks. It provides numerous features that ensure the data stored in it remains secure, consistent, and available. One of the most important features of PostgreSQL is the ability to manage active connections effectively.

In PostgreSQL, an active connection refers to a connection that is currently established with the server. Managing the active connections is crucial because it affects the performance and stability of the server. If the number of active connections surpasses the server's capacity, the server may become unresponsive, and users may experience issues with their applications.

PostgreSQL offers various tools and methods to manage active connections effectively. In this article, we will explore some of the most common ways to manage active connections, along with code examples.

Configuring Maximum Connections

The first and most crucial step in managing active connections is to configure the maximum number of connections that PostgreSQL can handle. The maximum connections can be set at the server level or per role basis. To set the maximum number of connections at the server level, follow the below steps:

1. Open the Postgres configuration file using a text editor. The location of the configuration file may vary depending on your PostgreSQL installation.

2. Search for the 'max_connections' parameter. Uncomment the line and set the desired number of connections.

3. Save the configuration file and restart the PostgreSQL server.

Example:

Maximum Connections

max_connections = 100

The above example sets the maximum number of connections to 100.

Monitoring Active Connections

Once the maximum connections have been configured, it is important to monitor the active connections to ensure that the server's resources are being utilized effectively. PostgreSQL provides several ways to monitor active connections:

1. Using psql

The psql command-line tool provides a simple and effective way to monitor active connections. Open a terminal and enter the following command:

psql -U postgres -c "SELECT * FROM pg_stat_activity;"

The above command will display detailed information about all active connections, including the client IP address, the query being executed, and the database being accessed.

2. Using pgAdmin

The pgAdmin graphical interface also provides a comprehensive way to monitor active connections. Open pgAdmin and connect to the PostgreSQL server. Right-click on the server name and select 'Activity'. The 'Current Activity' tab will display detailed information about all active connections.

Killing Active Connections

In some situations, it may become necessary to terminate an active connection. For example, if a client application becomes unresponsive, the connection can be terminated to free up server resources. PostgreSQL provides various methods to terminate an active connection.

1. Using psql

Open a terminal and enter the following command:

psql -U postgres -c "SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE pid <> pg_backend_pid() AND datname = '';"

Replace <database-name> with the name of the database where the active connection is established. The above command will terminate all active connections except the one where it is executed.

2. Using pgAdmin

Open pgAdmin and connect to the PostgreSQL server. Right-click on the active connection you want to terminate and select 'Cancel/terminate backend'. The active connection will be terminated immediately.

Connection Pooling

Connection pooling is a technique used to manage active connections by maintaining a pool of connections that can be reused by multiple client applications. Connection pooling provides several benefits, including reduced connection overhead and improved performance.

PostgreSQL supports various connection pooling tools, including PgBouncer and Pgpool-II.

1. Using PgBouncer

PgBouncer is a lightweight connection pooling tool that can handle a large number of connections simultaneously. To use PgBouncer, follow the below steps:

1. Install PgBouncer on the server where PostgreSQL is installed.

2. Configure PgBouncer by modifying the 'pgbouncer.ini' file. The configuration file is located in the PgBouncer installation directory.

3. Start the PgBouncer service by running the following command:

pgbouncer -d /path/to/pgbouncer.ini

4. Configure the client applications to connect to the PgBouncer server instead of the PostgreSQL server.

Example:

$ psql -h localhost -p 6432 -U postgres

The above example connects to the PgBouncer server running on the local host on port 6432.

2. Using Pgpool-II

Pgpool-II is a more advanced connection pooling tool that provides additional features, including load balancing and query routing. To use Pgpool-II, follow the below steps:

1. Install Pgpool-II on the server where PostgreSQL is installed.

2. Configure Pgpool-II by modifying the 'pgpool.conf' file. The configuration file is located in the Pgpool-II installation directory.

3. Start the Pgpool-II service by running the following command:

pgpool -d -f /path/to/pgpool.conf

4. Configure the client applications to connect to the Pgpool-II server instead of the PostgreSQL server.

Example:

$ psql -h localhost -p 9999 -U postgres

The above example connects to the Pgpool-II server running on the local host on port 9999.

Conclusion

Managing active connections in PostgreSQL is crucial for ensuring the performance and stability of the server. In this article, we explored various methods to manage active connections, including configuring maximum connections, monitoring active connections, killing active connections, and connection pooling. By implementing these techniques, administrators can effectively manage active connections in PostgreSQL and ensure its optimal performance.

Configuring Maximum Connections

Configuring the maximum number of connections is the first step in managing active connections in PostgreSQL. It determines how many connections can be established simultaneously with the server. The 'max_connections' parameter in the PostgreSQL configuration file is used to set the maximum number of connections. By default, PostgreSQL allows 100 connections per server, but it can be increased or decreased as per the requirement. Setting the maximum connections to a higher value than required can lead to memory and CPU exhaustion, whereas setting it too low can restrict the number of active connections.

Monitoring Active Connections

Monitoring active connections is crucial because it helps in identifying connection leaks and optimizing resource usage. PostgreSQL provides several methods for monitoring active connections, including monitoring with SQL commands and using graphical interfaces like pgAdmin. The 'pg_stat_activity' system view in PostgreSQL can be used to retrieve information such as client IP address, query being executed, and database being accessed for all active connections. Graphical interfaces like Pgadmin and command-line tools like psql can be used to retrieve this information and analyze the active connection usage.

Killing Active Connections

Terminating active connections is an essential task in managing connections when a particular connection is no longer required or causing issues. Killing an active connection releases the resources consumed by the idle connection. PostgreSQL provides two methods for killing active connections: using SQL commands and graphical tools like pgAdmin. SQL commands like 'pg_terminate_backend' and 'pg_cancel_backend' can be used to kill specific connections. Similarly, the PgAdmin graphical interface provides a more accessible method of canceling or terminating active connections.

Connection Pooling

Connection pooling is a technique used to manage active connections efficiently by reducing overhead and improving performance. Connection pooling allows multiple client applications to share a common pool of connections rather than creating a new connection for each client application. This reduces the number of active connections and optimizes resource utilization. PostgreSQL supports different types of connection pooling, including JDBC Connection Pooling, PgBouncer, and Pgpool-II. PgBouncer is a lightweight connection pooling tool that is easy to configure and provides high performance. Pgpool-II is a more advanced connection pooling tool that offers additional features such as load balancing and query routing.

In conclusion, active connections management is an essential task in PostgreSQL database administration to ensure optimal performance and stability of the system. PostgreSQL provides various methods to manage active connections, including configuring maximum connections, monitoring active connections, killing active connections, and connection pooling. By implementing these techniques, PostgreSQL administrators can ensure resource optimization, reduce connection overhead, and improve application performance.

Popular questions

1. What is the maximum number of connections allowed by default in PostgreSQL?
   Answer: The maximum number of connections allowed by default in PostgreSQL is 100 per server.

2. How can the maximum number of connections be set in PostgreSQL?
   Answer: The maximum number of connections can be set by modifying the 'max_connections' parameter in the PostgreSQL configuration file.

3. What system view can be used to monitor active connections in PostgreSQL?
   Answer: The 'pg_stat_activity' system view can be used to monitor active connections in PostgreSQL.

4. How can active connections be terminated in PostgreSQL?
   Answer: Active connections can be terminated in PostgreSQL using SQL commands like 'pg_terminate_backend' or using graphical tools like pgAdmin.

5. What is connection pooling, and what are some connection pooling tools available for PostgreSQL?
   Answer: Connection pooling is a technique used to optimize resource utilization and improve application performance by sharing a common pool of connections among multiple client applications. Some connection pooling tools available for PostgreSQL are JDBC Connection Pooling, PgBouncer, and Pgpool-II.

Tag

pg_connections