Wait Type HADR_LOGCAPTURE_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.

What is HADR_LOGCAPTURE_SYNC?

The HADR_LOGCAPTURE_SYNC wait type occurs when SQL Server is waiting for synchronization between the log capture process on the primary replica and the availability group’s secondary replicas. The log capture process is responsible for reading transaction logs on the primary replica and sending them to the secondary replicas to keep them synchronized.

In simpler terms, this wait type means SQL Server is ensuring the transaction logs are captured and sent to all replicas as part of the Always On synchronization process. While some wait time is normal, prolonged waits can indicate issues with your setup or workload.

Why Does HADR_LOGCAPTURE_SYNC Happen?

Several factors can contribute to HADR_LOGCAPTURE_SYNC waits, including:

• High transaction log activity on the primary replica, generating large amounts of log data to synchronize.
• Network latency or insufficient bandwidth between the primary and secondary replicas.
• Resource constraints on the primary or secondary replicas, such as CPU or disk I/O bottlenecks.
• Slow or delayed log application on the secondary replicas.
• Misconfigurations or suboptimal Always On settings for your workload.

Understanding and addressing these factors can help minimize the impact of this wait type on your system’s performance.

How to Monitor HADR_LOGCAPTURE_SYNC Waits

Monitoring HADR_LOGCAPTURE_SYNC waits can provide insights into how effectively your Always On Availability Group is synchronizing. The Database Health Monitor is an excellent tool for this purpose. Its Historic Waits Monitoring feature allows you to track this and other wait types over time, helping you identify patterns and correlate waits with specific system events or workloads.

By using Database Health Monitor, you can determine if these waits are caused by high transaction volume, resource constraints, or network issues, and take action to resolve the underlying problems.

What Can You Do About HADR_LOGCAPTURE_SYNC Waits?

If you encounter frequent or prolonged HADR_LOGCAPTURE_SYNC waits, consider the following actions:

• Optimize queries and indexes on the primary replica to reduce the volume of transaction log activity.
• Upgrade network bandwidth or optimize your network configuration to reduce latency between replicas.
• Ensure the primary and secondary replicas have adequate CPU, memory, and disk I/O resources to handle synchronization workloads.
• Review Always On Availability Group settings to ensure they align with best practices for your workload.
• Monitor and address slow log application on secondary replicas by optimizing their performance and resources.

These steps can help you reduce synchronization delays and improve the overall performance of your Always On environment.

How Stedman Solutions Can Help

At Stedman Solutions, we specialize in SQL Server performance tuning and troubleshooting, including resolving wait types like HADR_LOGCAPTURE_SYNC. Our managed services offer proactive monitoring and expert guidance to ensure your Always On Availability Groups are running smoothly. Additionally, our Database Health Monitor provides powerful tools for tracking and analyzing SQL Server waits, helping you maintain a high-performing and reliable database system.

If you’re experiencing performance challenges or need assistance optimizing your SQL Server setup, contact us today. Let us help you achieve a resilient and efficient SQL Server environment!

Find out more about our SQL Server Managed Services

Applies to

Related Waits

See Also

• More About HADR_LOGCAPTURE_SYNC