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Snowflake Dynamic Tables offer a powerful way to automate data transformations, ensuring that tables remain fresh and up to date. However, refresh failures can occur due to various reasons such as query errors, or resource constraints. To proactively monitor and respond to such failures, we can leverage Snowflake Alerts to send email notifications whenever a refresh fails. However, designing an efficient alerting mechanism is crucial to avoid redundant notifications while ensuring timely response to failures.
In this blog, we will explore two different alerting approaches for detecting dynamic table refresh failures, identify their limitations, and introduce a refined solution that ensures alerts are sent only when a new failure occurs after the last notification.
Scenario: Dynamic Table Refresh Monitoring with Alerts
Let’s assume we have a Dynamic Table CUST_ACCESSORY_DT that undergoes periodic refreshes. Our goal is to implement an alerting mechanism that:
✅ Detects refresh failures using DYNAMIC_TABLE_REFRESH_HISTORY.
✅ Sends an email notification whenever a failure occurs.
✅ Avoids sending duplicate notifications for the same failure.
Initial Approach: Basic Alert (Repeated Notifications)
The first approach is a straightforward Snowflake Alert that checks for any failures in the last one hour and triggers an email notification if a failure is detected.
Problem: Repeated Notifications
Problem: Repeated Notifications
- If a single failure occurs, the alert continues to send emails every minute until the failure record falls out of the one-hour window.
- This results in spammy notifications, even if no new failures have occurred.
Example Scenario
- 10:00 AM: A dynamic table refresh fails.
- 10:01 AM – 11:00 AM: The alert sends 59 emails (one every minute), even though the failure happened only once.
- 11:01 AM: The failure is no longer in the history window, and the alerts stop.
Issue: Too many notifications for a single failure!
As we can see the Alert sends an email every 1 minute even the failure in Dynamic table happened only once in last 1 hour.
Improved Approach: Smarter Alert (Only New Failures)
To avoid duplicate notifications, we modify the alert to only consider failures that occurred after the last successful alert execution.
Key Improvement: Reduced Redundant Emails
- This alert remembers the last successful notification time using SNOWFLAKE.ALERT.LAST_SUCCESSFUL_SCHEDULED_TIME().
- It only checks for failures that happened after the last alert execution.
- No duplicate emails are sent for old failures.
Example Scenario
- 10:00 AM: A dynamic table refresh fails → Email sent.
- 10:01 AM – 11:00 AM: No new failures occur → No emails sent.
- 11:10 AM: Another failure occurs → Email sent.
Benefit: Only new failures trigger an alert, reducing unnecessary notifications.
Conclusion:
- The initial approach provided basic monitoring but led to excessive notifications.
- The improved approach ensures alerts are sent only for new failures, making the system more efficient.
- Key takeaway: Use SNOWFLAKE.ALERT.LAST_SUCCESSFUL_SCHEDULED_TIME() to avoid duplicate alerts!
