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Is Auto Update statistics asynchronously enabled?
If we enable the Auto Update Statistics Asynchronously, SQL Server does not wait to update the statistics. The next executed query takes the benefit of the updated statistics. Since SQL Server does not wait for the updated statistics, we also call it Asynchronous mode statistics.
How to set Auto Update statistics in SQL Server?
To set the asynchronous statistics update option in SQL Server Management Studio, in the Options page of the Database Properties window, both Auto Update Statistics and Auto Update Statistics Asynchronously options need to be set to True. Statistics updates can be either synchronous (the default) or asynchronous.
How are Statistics updated in SQL Server async?
New behavior is enabled with the ASYNC_STATS_UPDATE_WAIT_AT_LOW_PRIORITY database-scoped configuration . By default, the SQL Server database engine updates statistics automatically as needed to reflect changes in the underlying data, and help the query optimizer generate more optimal plans.
How does async stats update at low priority work?
The ASYNC_STATS_UPDATE_WAIT_AT_LOW_PRIORITY configuration has no effect on that process. However, this configuration, if enabled on a secondary replica, applies to temporary statistics in the same fashion as it does to permanent statistics on the primary.
When does asynchronous statistics update cause a blocking chain?
An illustration of a blocking chain forming when asynchronous statistics update is waiting for a Sch-M lock at normal priority. The impact of this blocking chain could be severe, especially with frequent (re)compilations and statistics updates. For some workloads we have seen, blocking would not resolve for several minutes.
How to improve concurrency of asynchronous statistics update?
The new option to wait for lock at low priority in asynchronous statistics update solves a specific type of workload concurrency problem that has been affecting several Azure SQL and SQL Server customers. This solution is now available in Azure SQL Database and Azure SQL Managed Instance, and is planned to be included in SQL Server vNext.