Common Causes and Troubleshooting Solutions for SQL AG Data Synchronization Latency

This article summarizes the common causes , solutions and troubleshooting mechanism for SQL Availability Group (AG) data synchronization latency between primary and secondary for both synchronous-commit and asynchronous-commit mode.


The latency commonly happens at log harden phase or log redo phase. And sometimes, both. If it happens at log harden phase, you will likely to see HADR_SYNC_COMMIT wait type in your primary that waiting for your synchronous-commit secondary replica’s acknowledgement. Also, your primary is likely to encounter latency on committing transactions sent from application because of this wait.  If latency happens purely at log redo phase, you are likely