When it comes to optimizing the performance of a SQL Server database, one of the key areas to focus on is creating efficient indexes. Indexes have been a topic of debate and interest in the industry for over two decades, and their importance in building highly performant SQL Server applications cannot be overstated.
SQL Server is a cost-based optimizer, which means it does a good job of identifying, evaluating, and using the right index based on your query needs. However, it is also important for administrators to monitor how indexes are being used in a database. This includes identifying and eliminating unwanted and duplicate indexes created by developers.
One way to monitor index usage is through the use of three reports available under the Database node in SQL Server. These reports provide valuable information about index operational statistics, index physical statistics, and user statistics.
Index Usage Statistics
The Index Usage Statistics report provides information about index operational statistics and usage statistics. This includes details about scans, seeks, last access time, and the number of user scans. The report uses queries that retrieve data from the sys.dm_db_index_operational_stats and sys.dm_db_index_usage_stats dynamic management views.
By analyzing this report, you can determine which indexes are being used by various queries and whether they are performing seeks or scans. It is generally preferable to see seeks rather than scans, especially for large tables. If an index is not shown in this report, it means that no query has been executed that can utilize that index. However, it is important not to drop indexes solely based on the assumption that they are not being used, as there may be queries in the future that can benefit from them.
Index Physical Statistics
The Index Physical Statistics report provides insights into how indexes are physically laid out on data files. The report includes information such as index fragmentation, object names, index types, and recommendations for rebuilding or reorganizing indexes. The report uses the sys.dm_db_index_physical_stats dynamic management view to retrieve this information.
It is important to note that the recommendation for rebuilding or reorganizing an index is based on the level of fragmentation, but it does not consider the size of the table. Therefore, it is recommended to click on the “+” symbol in the report to view the size of the table before deciding whether to rebuild or reorganize the index. In some cases, even if the index has low fragmentation, it may still be recommended to rebuild it if the table is small.
User Statistics
The User Statistics report, although not directly related to indexes, provides valuable information about the users connected to the database. This report is particularly useful in situations where multiple applications use different logins to connect to the SQL Server instance. The report includes details such as login names, session IDs, connection counts, request counts, cursor counts, transaction counts, CPU time, memory usage, and more. The report retrieves data from the sys.dm_exec_sessions, sys.dm_exec_connections, and master..sysprocesses system views.
By analyzing this report, you can gain insights into the usage patterns of different users and identify any potential performance bottlenecks caused by excessive resource consumption.
Understanding and effectively utilizing these reports can greatly contribute to the performance tuning efforts of your SQL Server database. By monitoring index usage, optimizing index physical layout, and analyzing user statistics, you can ensure that your database performs at its best.
Thank you for reading this blog post. We hope you found it informative and that it helps you in your SQL Server performance tuning endeavors.