Start Updating a table from another table in sql server

Updating a table from another table in sql server

Index maintenance and statistics: The distribution of data is not altered when an index is rebuilt or reorganised so there is no requirement for statistics to be updated as a result of these operations.

Using the auto update async option should ameliorate this issue by spawning the update onto a background thread while the original query proceeds with the stale stats. The threshold at which a statistic is declared stale for tables greater than 500 rows is 500 20% of total rows. Highly skewed updates can cause statistics to become misleading long before this threshold is reached.

I’ve been looking into the behaviour of statistics in SQL Server 2008 – so I’d like to present an overview from a DBA perspective. Statistics are a database scoped object that are used by the query optimiser in creating query plans.

They describe the distribution of values in a column or columns and help the optimiser choose indexes to use.

And an individual statistics object, the so-called stat blob, can be examined using DBCC SHOW_STATISTICS().

Have a look at the links at the end of this post if you want to know more detail about the data surfaced by DBCC SHOW_STATISTICS().

The automatic updating behaviour can be overridden at a statistic level by using the NORECOMPUTE option with the CREATE or UPDATE STATISTICS statements or by using sp_autostats.

This will show the auto update status of all indexes on a given table or indexed view: You can disable automatic updating for individual statistics if this is enabled at the database level.

If resample is not specified the default sample rate calculations are used.