Wait Type ASYNC_OP_COMPLETION

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.

ASYNC_OP_COMPLETION is a wait type that is generated when a task is waiting for the completion of an asynchronous operation. An asynchronous operation is one that occurs in the background and does not block the execution of other tasks. In SQL Server, these operations are typically related to I/O (input/output) operations, such as reading or writing data to a disk.

When a task is waiting for an asynchronous operation to complete, it will enter a "waiting" state and will not be able to do any work until the operation has finished. This can cause delays in the execution of the task and may affect the overall performance of the database.

The ASYNC_OP_COMPLETION wait type is typically not a cause for concern, as it is a normal part of the operation of the database. However, if a task is spending a significant amount of time waiting for asynchronous operations to complete, it may be an indication that there is an issue with the I/O system or that the database is not being optimized properly.

To troubleshoot issues related to the ASYNC_OP_COMPLETION wait type, it may be necessary to examine the I/O system and the configuration of the database. This may include optimizing the placement of data files on the disks, improving the hardware configuration of the disks, or modifying the database design to reduce the number of I/O operations that are required.

In summary, the ASYNC_OP_COMPLETION wait type is a normal part of the operation of SQL Server and is generated when a task is waiting for the completion of an asynchronous operation. If a task is spending a significant amount of time waiting for these operations to complete, it may be an indication that there is an issue with the I/O system or the database configuration. By examining the I/O system and optimizing the database, it is possible to improve the performance of the database and reduce the amount of time spent waiting for asynchronous operations to complete.

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Applies to

Related Waits

See Also

• More About ASYNC_OP_COMPLETION