Database & SQL
PostgreSQL Replication Lag Calculator
Enter replication lag in bytes and WAL generation rate to compute lag in seconds, failover RPO risk, and synchronous vs asynchronous replication tradeoffs.
No data is transmitted — everything runs locallyTool
About this tool
PostgreSQL Replication Lag Calculator
The PostgreSQL Replication Lag Calculator converts WAL lag bytes to seconds, computes failover RPO, and compares synchronous vs asynchronous replication tradeoffs.
• Convert pg_stat_replication lag bytes to seconds for an SLA report
• Calculate failover RPO data loss risk from current async replication lag
• Determine whether synchronous replication overhead is justified by RPO requirements
• Alert threshold: compute the lag bytes equivalent of a 30-second lag for a Better Stack monitor
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Uptime, incident, and on-call management. Better Stack provides status pages, incident management, and on-call scheduling for engineering teams.
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FAQ
What does this tool tell you?
The PostgreSQL Replication Lag Calculator converts WAL lag bytes to seconds, computes failover RPO, and compares synchronous vs asynchronous replication tradeoffs.
What affects the result most?
Replication lag = current_wal_lsn - replay_lsn on replica — measured in bytes and seconds. Bytes lag to seconds: bytes_behind / average_wal_generation_rate (bytes/second). Synchronous vs asynchronous replication: sync = zero data loss but adds commit latency.
How should I use the result?
The calculation is deterministic — the same inputs always produce the same output — so the most useful workflow is to vary one input at a time and see which factor moves the result most. That tells you where to focus your attention before committing to a decision.