Index optimization is a crucial aspect of SQL Server performance tuning. When faced with queries that are running slow or tables that need optimization, there are certain steps you can take to improve query speed. Before diving into the more complex optimization techniques, it’s important to follow a basic checklist that can often yield significant improvements. Here are some key points to consider:
- Create indexes on frequently used columns in your T-SQL code. Columns used in WHERE, ORDER BY, and GROUP BY clauses are good candidates for indexes.
- Create indexes on columns used in JOIN conditions. This can greatly enhance the performance of queries involving multiple tables.
- Remove any unnecessary indexes. Indexes take up hard drive space and can slow down insert, update, and delete operations. It’s important to regularly review and remove indexes that are no longer needed.
- Smaller index keys generally perform better than larger ones. If possible, consider using integer columns instead of varchar columns for indexing.
- Ensure that a clustered index exists before creating non-clustered indexes. A clustered index should be created on a single, unchanging, and narrow column. The primary key is often the best candidate for a clustered index.
- Non-clustered indexes can improve query performance for queries that return fewer rows and have a wide selectivity spectrum.
- Each table should have one clustered index.
- Avoid creating indexes on columns with low selectivity. This can slow down row modifications and provide little benefit to the system.
- When creating a multiple column index or a covered index, order the columns from most selective on the left to gradually decreasing selectivity on the right.
- If the tempdb is on different disks, consider using the SORT_IN_TEMPDB option when creating tables. This can improve index creation performance.
- Regularly rebuild indexes using the ALTER INDEX statement and defragment indexes to maintain optimal performance.
By following this checklist, you can significantly improve the performance of your SQL Server queries and optimize the use of indexes. However, it’s important to note that index optimization is an ongoing process that requires experimentation and experience to achieve the best results.
For a more detailed checklist on SQL Server index optimization, you can download the SQL Server Index Optimization Checklist.