How Can I Reliably Send Emails Triggered by PostgreSQL Database Events?

Sending Emails from PostgreSQL Triggers: A Detailed Walkthrough

You've encountered a specific scenario where you need to trigger an email send when a certain field in the dataset table is updated to "Finished." Let's break down the suggested solution and provide a more comprehensive understanding.

The Drawbacks of Direct Database Email Sending

Sending emails directly from a database trigger can be problematic for various reasons. Delays in DNS resolution or mail server issues can lead to database sessions hanging, potentially causing connection issues.

The Recommended Approach: Using a Listener Queue

Instead, it's recommended to have the trigger NOTIFY a separate helper script that runs continuously and listens to the database. Here's how the process would work:

1. Trigger Inserts Row into Queue: When the trigger detects that the publisher field has changed to "aaaa," it inserts a row into a designated queue table and sends a NOTIFY message.
2. Helper Script Receives NOTIFY Message: A Python script using the psycopg2 library registers to LISTEN for the NOTIFY message. Upon receiving it, the script examines the queue table for new items.
3. Script Sends Email: The script extracts the necessary information from the database and formats it into an email template. It then connects to the mail server and sends the email based on the provided template.
4. Queue Table Management: Once the email has been successfully sent, the script removes the corresponding row from the queue table. This ensures that if there are any temporary email delivery issues, the email will continue to be attempted until it succeeds.

Alternatives to the Listener Queue

If using a listener queue is not feasible for your case, you can consider using PgMail, a PostgreSQL extension specifically designed for sending emails from the database.

Conclusion

By utilizing the proposed approach, you can efficiently trigger email sends from PostgreSQL, ensuring that emails are delivered reliably without the potential pitfalls of direct database email sending.

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