Tag Archives: sys.indexes

Database Statistics Health and Update Scripts

Posted by on January 14, 2016 Comments Off on Database Statistics Health and Update Scripts

I like using Ola Hallengren’s maintenance scripts. Super configuratible, logging, SQl Agent job creation and etc. Sometimes I want to spot check on some of the statistics. Stale statistics can cause cardinality issues with SQL plans.

We learn how database statistics are used:
“The query optimizer uses statistics to create query plans that improve query performance. For most queries, the query optimizer already generates the necessary statistics for a high quality query plan; in a few cases, you need to create additional statistics or modify the query design for best results. This topic discusses statistics concepts and provides guidelines for using query optimization statistics effectively.”

The sample rate is set to full s or 100 percent of the rows will be scanned. A full scan will create overhead.  Need to always look at the impact to your environment. You could have old statistics and not used or duplicate statistics.  In some cases, the higher sample rate can actually cause the plan be less optimal.

Rule of thumb, your queries will perform better with fresh statistics.

I have two scripts to I use to find the health of statistics and update statistics based upon certain criteria.
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Simple Index Usage Query

Posted by on December 27, 2015 Comments Off on Simple Index Usage Query

Yes, another index usage query. I adapted this a tiny bit to add a time element to it. DMVs will flush out any information when the services are restarted. I omitted system usage information to gear it more toward user created objects. Also, added the users statistics together to get a better Idea of total usage. It gives the user a good starting point to see utilization of current indexing. Conversely, Microsoft provides a “Missing indexes” DMV named sys.dm_db_missing_index_details. Don’t have blind faith in the suggestions. They are based on specific activity since last restart.
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