When To Update Statistics?
if and only if auto update statistics feature is not good enough for your requirements.
i mean if auto create and auto update statistics are ON and you are getting a bad query plan because the statistics are not accurate or current then it might be a good idea to have control over statistics creation and update.
but if you are fine with your sql server performance and Query execution times.
then i suggest stopping the Updates Statistics command from your Maintenance Plans
updating statistics is important and useful
1. allows the SQL Server query optimizer to produce good query plans consistently, while keeping development and administration costs low
2. Statistics are used by the query optimizer to estimate the selectivity of expressions, and thus the size of intermediate and final query results.
3. Good statistics allow the optimizer to accurately assess the cost of different query plans and then choose a high-quality plan
If you want to do update Statistics manually you should first know When Statistics are updated automatically
If the SQL Server query optimizer requires statistics for a particular column in a table that has undergone substantial update activity since the last time the statistics were created or updated, SQL Server automatically updates the statistics by sampling the column values (by using auto update statistics). The statistics auto update is triggered by query optimization or by execution of a compiled plan, and it involves only a subset of the columns referred to in the query. Statistics are updated before query compilation if AUTO_UPDATE_STATISTCS_ASYNC is OFF
here are nice articles that speak about when update statistics is triggered in SQL server
- from sqlstatistics
- from simple-talk Section 13. When is the Auto-Update to Statistics Triggered?
- support.microsoft Section: Automating Autostats determination
- msdn.microsoft section: Maintaining Statistics in SQL Server 2008
after knowing when statistics is triggered it will help you decide when to update statistics manually
to know more about Statistics & its effect on performance i recommend BrentOzar and Kimberly in sqlskills very good blogs & bloggers.