Ms sql updating statistics


09-Jun-2020 12:55

One way to find out if your statistics are stale is to look at the execution plans and if you estimated rows greatly differ from your actual rows returned then that is a good indication that the interval needs to be upped.

In your case, you're going the other way and a bit of trial may be in order for you.

Exactly how often you should be updating statistics depends greatly on how much data modification your indexes and data is receiving.

If there is very little modification () to the data, then you could have a more infrequent schedule for the update statistics job.

Statistics are used by the query optimizer to estimate the selectivity of expressions, and thus the size of intermediate and final query results. 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.

If a query predicate contains a column with statistics, the Query Optimizer does not have to estimate the number of rows affected by that query, thus the Query Optimizer has enough information to create the execution plan.They are created on columns that do not have a histogram in an existing statistics object.The name of the auto-created statistics includes the column name and the object ID in hexadecimal format: _WA_Sys_.We recommend not updating statistics too frequently because there is a performance tradeoff between improving query plans and the time it takes to recompile queries. UPDATE STATISTICS can use tempdb to sort the sample of rows for building statistics.

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Could you please describe what are the benefits of using the Auto Create Statistics and Auto Update Statistics options?



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