I want to have it about a new database-setting in Sql Server 2005: Asynchronous Statistics Updates
Statistics are very important for the optimizer. The optimizer needs this information to decide which indexes to use or not. It is on basis of the statistics that an optimal execution plan is created.
Now, if there are enough data changes (approximately 20% of the data), it is possible that statistics are updated at the moment a new query is to be resolved (if database-setting auto-update statistics is on), possibly causing this query (the user) to wait until the statistics are updated and an optimal execution plan can be constructed.
This "synchronous" behaviour can be avoided with the database-setting "Asynchronous Statistics Updates". It is off by default. The setting can on-line be changed.
DDL: ALTER DATABASE YourDB SET AUTO_UPDATE_STATISTICS_ASYNC ON
We did not have the time to do performance comparison-tests.
If you want to read more in BOL, look for "Asynchronous statistics updates (SQL Server)".
Other information: www.microsoft.com/technet/prodtechnol/sql/2005/qrystats.mspx