Wait Type DBSEEDING_FLOWCONTROL

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 wait types provide crucial insights into what tasks are experiencing delays. One such wait type, DBSEEDING_FLOWCONTROL, is associated with Always On Availability Groups. This wait type appears when SQL Server is managing the flow of data during the initial seeding of a database in an Availability Group. In this post, we’ll break down what DBSEEDING_FLOWCONTROL means, when it occurs, and how it may impact performance.

What Is the DBSEEDING_FLOWCONTROL Wait Type?

The DBSEEDING_FLOWCONTROL wait type occurs when SQL Server is throttling the data transfer during database seeding in an Always On Availability Group. Seeding is the process of initializing a new secondary replica by copying the primary database’s data to the secondary replica. SQL Server uses flow control to prevent overwhelming the network or storage systems during this data transfer.

This wait type indicates that SQL Server is intentionally slowing down the data transfer to maintain system stability and ensure that the primary and secondary replicas remain responsive to other workloads.

When Does DBSEEDING_FLOWCONTROL Appear?

DBSEEDING_FLOWCONTROL waits are specific to the seeding process in Always On Availability Groups. You may encounter this wait type in the following scenarios:

• Adding a New Secondary Replica – When a new replica is being added to an Availability Group and database seeding is required.
• Automatic Seeding – When automatic seeding is configured, SQL Server handles the entire process of copying the database to the secondary replica.
• Large Databases – For large databases, flow control is more likely to occur to prevent overwhelming system resources during the transfer.

Why DBSEEDING_FLOWCONTROL Waits Matter

While some DBSEEDING_FLOWCONTROL waits are normal and expected during database seeding, prolonged or frequent waits can slow down the process. This can delay the Availability Group from reaching a synchronized state and may impact performance if other workloads are affected.

Common causes of prolonged DBSEEDING_FLOWCONTROL waits include:

• Network Bandwidth Limitations – Insufficient network capacity can cause flow control to engage more frequently to avoid overwhelming the network.
• Storage Performance Issues – Slow disk writes on the secondary replica can delay data transfer and trigger flow control.
• Large Database Sizes – Larger databases require more data to be transferred, increasing the likelihood of flow control.

How to Address DBSEEDING_FLOWCONTROL Waits

If DBSEEDING_FLOWCONTROL waits are slowing down the seeding process or affecting performance, consider these strategies:

• Optimize Network Performance – Ensure sufficient network bandwidth between the primary and secondary replicas. Use dedicated high-speed connections for Availability Group traffic.
• Upgrade Storage Performance – Use faster storage, such as SSDs, for the secondary replica to handle incoming data more efficiently.
• Seed During Off-Peak Hours – Perform seeding operations during periods of low system activity to minimize the impact on other workloads.
• Use Backup and Restore – For very large databases, consider manually seeding the secondary replica by restoring a backup, which can be faster and more efficient than automatic seeding.
• Monitor Seeding Progress – Use the Always On Dashboard or views like sys.dm_hadr_automatic_seeding to track the seeding process and identify bottlenecks.

Monitoring DBSEEDING_FLOWCONTROL Waits

To monitor DBSEEDING_FLOWCONTROL waits, use SQL Server’s sys.dm_os_wait_stats to analyze wait statistics. Combine this with Always On-specific views, such as sys.dm_hadr_database_replica_states, to get a complete picture of your Availability Group’s health and progress.

Conclusion

The DBSEEDING_FLOWCONTROL wait type in SQL Server is a normal part of the database seeding process in Always On Availability Groups. While these waits help maintain system stability during data transfer, prolonged waits may indicate network, storage, or system configuration issues. By optimizing network and storage performance, monitoring seeding progress, and scheduling operations during off-peak hours, you can minimize DBSEEDING_FLOWCONTROL waits and ensure a smooth seeding process.

For expert assistance with Always On Availability Groups, database seeding, or SQL Server performance tuning, Stedman Solutions offers managed services to help you maintain a reliable and efficient SQL Server environment.

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Applies to

Related Waits

See Also

• More About DBSEEDING_FLOWCONTROL