SQL Server Indexes Best Practices

Best Practices for Index Design

Effective index design balances query speed with system resource usage.

Consider the following when creating indexes:

• Analyze query workload to identify columns frequently used in WHERE, JOIN, ORDER BY clauses.
• Create indexes on columns with high selectivity to maximize filtering efficiency.
• Limit the number of indexes to avoid excessive overhead on data modifications.
• Use included columns to cover queries and reduce lookups.
• Prefer narrow indexes with fewer columns to reduce storage and improve maintenance.

Index Maintenance and Monitoring

Indexes require regular maintenance to prevent fragmentation and performance degradation.

Monitoring index usage helps identify unused or redundant indexes.

• Rebuild indexes when fragmentation exceeds 30% to reorganize data pages.
• Reorganize indexes for fragmentation between 5% and 30% to defragment without locking.
• Use SQL Server Dynamic Management Views (DMVs) to monitor index usage and fragmentation.
• Drop indexes that are rarely used to reduce overhead.
• Schedule maintenance during low-usage periods to minimize impact.

Avoiding Common Indexing Pitfalls

Certain mistakes can reduce the effectiveness of indexes or harm performance.

• Creating indexes on low-selectivity columns like gender or boolean flags.
• Over-indexing tables with many indexes causing slow inserts, updates, and deletes.
• Ignoring index fragmentation leading to slower query execution.
• Not updating statistics, which can cause inefficient query plans.
• Using indexes without considering the impact on write-heavy workloads.