Database Replication Lag Helper

Summary

Enter your write rate and SLA to get the max tolerable replication lag, estimated data-loss window, and bytes at risk.

How it works

1. Enter the average write throughput of your primary database (rows/sec or MB/sec).
2. Set your RPO — the maximum data loss your SLA or business allows (in seconds).
3. Optionally set an alert threshold as a percentage of RPO to get an early-warning lag value.
4. The tool computes the max acceptable lag, bytes at risk at that lag, and the alert trigger point.
5. Use the results to configure replica monitoring alerts (e.g., in Prometheus, Datadog, or CloudWatch).
6. Adjust write rate or RPO to model different failure scenarios or SLA tiers.

Use cases

• Set Prometheus replication_lag alert thresholds backed by SLA data.
• Estimate worst-case data loss before promoting a read replica during failover.
• Validate whether a replica is safe to use as a backup source.
• Model the impact of adding a cross-region replica with higher network latency.
• Communicate data-loss risk to stakeholders in concrete seconds and megabytes.
• Compare RPO cost across sync vs async replication modes.
• Size your binary log or WAL retention to cover the acceptable lag window.
• Audit existing alert thresholds against updated SLA commitments.

Frequently Asked Questions