How to use the command 'pg_isready' (with examples)

The pg_isready command is a utility that comes with PostgreSQL installations, designed to quickly check the connectivity and readiness of a PostgreSQL server. It is a simple yet effective command that helps database administrators and users determine if a PostgreSQL server is up and responding to connection requests. This tool offers several options to customize the checks according to the specific needs, such as specifying hostnames, ports, database names, and more.

Use case 1: Check connection

Code:

pg_isready

Motivation: In many situations, particularly during service maintenance or after server startup, it is essential to verify immediately if the PostgreSQL server is up and running. By executing the simple pg_isready command, you can quickly determine the server’s readiness without involving complex scripts or client interactions. This allows for streamlined start-up checks and is particularly useful in automated scripts where a quick, affirmative response about server availability is required.

Explanation: The command pg_isready alone checks the default settings for connecting to a PostgreSQL server. It doesn’t require any additional parameters or arguments as it references the default socket and port (usually port 5432) configured during the PostgreSQL installation. It implies that you have localhost access set up for your database.

Example output:

/var/run/postgresql:5432 - accepting connections

This output signifies that the PostgreSQL server located on localhost at the default port 5432 is active and accepting connections.

Use case 2: Check connection with a specific hostname and port

Code:

pg_isready --host=hostname --port=port

Motivation: In distributed systems or environments where multiple servers are involved, PostgreSQL may be hosted on a separate node or use a non-default port. The --host and --port options allow a user to specify the exact target server and port to check its readiness. This is crucial for database administrators aiming to ensure connectivity from different network segments or when dealing with multiple PostgreSQL instances running on different configurations.

Explanation:

• --host=hostname specifies the domain name or IP address of the server you want to check. This replaces the command’s default behavior of checking the local host.
• --port=port indicates the network port of the PostgreSQL server. If your server runs on a port other than the default 5432, this option becomes necessary.

Example output:

hostname:port - accepting connections

This signifies that the server at the specified hostname and port is accessible and ready for connection attempts.

Use case 3: Check connection displaying a message only when the connection fails

Code:

pg_isready --quiet

Motivation: In situations where the noise from regular status checks is undesirable, especially in a well-functioning system or during log reviews, you may only want to be notified of issues. The --quiet flag is beneficial in scripts or monitoring tools where only failure conditions (errors) should trigger alerts or logs. This reduces the clutter of messages and focuses attention only on when an action needs to be taken due to connection failure.

Explanation: --quiet suppresses output unless an error occurs. If the server is running smoothly, no output is produced, streamlining system monitoring and allowing easier identification of issues at a glance.

Example output (upon failure):

no response

This output indicates that the server isn’t responding as expected, and some intervention might be needed to resolve connection issues.

Conclusion:

The pg_isready utility is a straightforward yet powerful command that offers a lightweight solution for checking PostgreSQL server availability. Whether it’s validating default connections, specifying detailed server connection parameters, or reducing output to critical failures, this command is a versatile tool that serves various needs in maintaining PostgreSQL databases. Through understanding and utilizing these specific use cases, database administrators and developers can ensure the readiness and reliability of their PostgreSQL servers effectively.