Wait Type HADR_TRANSPORT_SESSION

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 depend on seamless communication between replicas to ensure data consistency and high availability. During this communication, certain wait types like HADR_TRANSPORT_SESSION can occur. Understanding this wait type can help you identify and address potential bottlenecks in your Always On environment.

What is HADR_TRANSPORT_SESSION?

The HADR_TRANSPORT_SESSION wait type occurs when SQL Server is managing the communication sessions required for Always On Availability Groups. These sessions handle the transport of transaction logs and other critical data between the primary and secondary replicas. This wait indicates that SQL Server is waiting for tasks related to these communication sessions to complete.

In simpler terms, this wait type shows that SQL Server is managing the flow of data between replicas to keep them synchronized. While some waits are normal, frequent or prolonged waits may point to underlying network or configuration issues.

Why Does HADR_TRANSPORT_SESSION Happen?

Several factors can lead to HADR_TRANSPORT_SESSION waits, including:

• Network latency or bandwidth limitations affecting data transmission between replicas.
• High transaction log activity on the primary replica generating large amounts of data to synchronize.
• Resource bottlenecks, such as limited CPU, memory, or disk I/O on primary or secondary replicas.
• Configuration issues in the Always On Availability Group setup.
• Contention or bottlenecks in the transport layer managing replica communication.

Understanding these factors is crucial for resolving synchronization delays and optimizing Always On performance.

How to Monitor HADR_TRANSPORT_SESSION Waits

Monitoring HADR_TRANSPORT_SESSION waits is essential for diagnosing communication issues in Always On Availability Groups. The Database Health Monitor is an excellent tool for this purpose. Its Historic Waits Monitoring feature allows you to track when these waits occur, how often they happen, and their impact on system performance.

Using Database Health Monitor, you can identify patterns and determine whether these waits are caused by network constraints, resource limitations, or workload imbalances, enabling you to take targeted action to optimize your environment.

What Can You Do About HADR_TRANSPORT_SESSION Waits?

If you notice frequent or prolonged HADR_TRANSPORT_SESSION waits, consider the following actions:

• Ensure your network infrastructure has sufficient bandwidth and low latency to support data transport between replicas.
• Optimize workloads on the primary replica to reduce transaction log activity and improve synchronization performance.
• Allocate adequate CPU, memory, and disk I/O resources to both primary and secondary replicas.
• Review and adjust Always On configurations, such as synchronization modes, to align with your workload requirements.
• Analyze and address network traffic contention to improve overall data transport efficiency.

These steps can help you minimize transport session waits and improve the reliability of your Always On Availability Groups.

Why Use Database Health Monitor?

The Database Health Monitor is a comprehensive tool for tracking SQL Server wait types, including HADR_TRANSPORT_SESSION. Its Historic Waits Monitoring feature provides valuable insights into wait trends, helping you identify and resolve bottlenecks in Always On synchronization processes. With Database Health Monitor, you can ensure your SQL Server environment operates at peak performance.

Start using Database Health Monitor today to monitor and optimize your SQL Server’s performance, keeping your Always On Availability Groups running smoothly!

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Applies to

Related Waits

See Also

• More About HADR_TRANSPORT_SESSION