Wait Type HADR_PARTNER_SYNC

Wait statistics, in the context of SQL Server, refer to the amount of time that a query spends waiting to access data in the database. When a client application requests data from the database, the request is placed in a queue and the client application must wait for its turn to access the data. The time that the query spends waiting is called a "wait" and is tracked by SQL Server. This information can be used to identify potential performance bottlenecks and optimize the performance of the database. Wait statistics are commonly used by database administrators to diagnose and troubleshoot performance issues in SQL Server.

SQL Server Always On Availability Groups rely on synchronization between replicas to ensure high availability and disaster recovery. Occasionally, you may encounter wait types like HADR_PARTNER_SYNC, which provide insight into synchronization activities and potential performance bottlenecks. Knowing what this wait type means can help you maintain a reliable and efficient Always On setup.

What is HADR_PARTNER_SYNC?

The HADR_PARTNER_SYNC wait type occurs when SQL Server is waiting for synchronization between the primary replica and a partner replica in an Always On Availability Group. This wait type indicates that SQL Server is working to ensure all changes made on the primary replica are transmitted and acknowledged by the partner replica.

In simpler terms, this wait type reflects the time SQL Server spends ensuring that replicas are in sync and consistent. While some occurrences of this wait type are normal, frequent or prolonged waits may indicate network, resource, or configuration issues.

Why Does HADR_PARTNER_SYNC Happen?

Several factors can lead to HADR_PARTNER_SYNC waits, including:

• High transaction log activity on the primary replica, generating a large amount of data to be synchronized.
• Network latency or insufficient bandwidth between the primary and partner replicas.
• Resource bottlenecks, such as limited CPU, memory, or disk I/O, on either the primary or secondary replicas.
• Slow or delayed log application on the partner replica.
• Suboptimal Always On Availability Group configurations or synchronization modes.

Addressing these factors can help reduce synchronization delays and improve the performance of your Always On environment.

How to Monitor HADR_PARTNER_SYNC Waits

To track and analyze HADR_PARTNER_SYNC waits effectively, using a monitoring tool like Database Health Monitor is essential. Its Historic Waits Monitoring feature provides detailed insights into when these waits occur, their frequency, and correlations with system activity.

Database Health Monitor helps you identify patterns in synchronization delays and pinpoint the root causes, enabling you to take corrective actions to optimize your Always On setup.

What Can You Do About HADR_PARTNER_SYNC Waits?

If you experience frequent or prolonged HADR_PARTNER_SYNC waits, consider the following steps:

• Optimize queries and indexes on the primary replica to reduce transaction log generation.
• Improve network bandwidth and reliability between replicas to reduce latency.
• Ensure adequate CPU, memory, and disk I/O resources on both the primary and partner replicas.
• Review Always On Availability Group configurations to ensure synchronization modes align with your workload and performance needs.
• Monitor and optimize the performance of secondary replicas to prevent delays in log application.

Implementing these measures can help minimize synchronization delays and improve the overall performance of your Always On Availability Groups.

How Stedman Solutions Can Help

At Stedman Solutions, we specialize in SQL Server performance optimization and troubleshooting, including resolving wait types like HADR_PARTNER_SYNC. Our managed services provide proactive monitoring and expert guidance to ensure your Always On Availability Groups are running efficiently. Additionally, our Database Health Monitor offers comprehensive tools for tracking and analyzing SQL Server waits, helping you maintain a reliable and high-performing database environment.

If you’re facing challenges with Always On synchronization or need assistance optimizing your SQL Server, contact us today. Let us help you achieve a resilient and efficient database system!

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Applies to

Related Waits

See Also

• More About HADR_PARTNER_SYNC