IF Auto Update Statistics ENABLED in Database Design, Why we need to Update Statistics as a maintenance plan

Hi Experts,
IF Auto Update Statistics ENABLED in Database Design, Why we need to Update Statistics as a maintenance plan for Daily/weekly??
Vinai Kumar Gandla

Hi Vikki,
Many systems rely solely on SQL Server to update statistics automatically(AUTO UPDATE STATISTICS enabled), however, based on my research, large tables, tables with uneven data distributions, tables with ever-increasing keys and tables that have significant
changes in distribution often require manual statistics updates as the following explanation.
1.If a table is very big, then waiting for 20% of rows to change before SQL Server automatically updates the statistics could mean that millions of rows are modified, added or removed before it happens. Depending on the workload patterns and the data,
this could mean the optimizer is choosing a substandard execution plans long before SQL Server reaches the threshold where it invalidates statistics for a table and starts to update them automatically. In such cases, you might consider updating statistics
manually for those tables on a defined schedule (while leaving AUTO UPDATE STATISTICS enabled so that SQL Server continues to maintain statistics for other tables).
2.In cases where you know data distribution in a column is "skewed", it may be necessary to update statistics manually with a full sample, or create a set of filtered statistics in order to generate query plans of good quality. Remember,
however, that sampling with FULLSCAN can be costly for larger tables, and must be done so as not to affect production performance.
3.It is quite common to see an ascending key, such as an IDENTITY or date/time data types, used as the leading column in an index. In such cases, the statistic for the key rarely matches the actual data, unless we update the Statistic manually after
every insert.
So in the case above, we could perform manual statistics updates by
creating a maintenance plan that will run the UPDATE STATISTICS command, and update statistics on a regular schedule. For more information about the process, please refer to the article:
https://www.simple-talk.com/sql/performance/managing-sql-server-statistics/
Regards,
Michelle Li

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