Duplicate or Overlapping Indexes

Indexes are essential for optimizing SQL Server database performance, but having duplicate or overlapping indexes can add unnecessary complexity and increase maintenance overhead. These redundant indexes often provide no additional performance benefit and can degrade efficiency by forcing the query optimizer to evaluate more options than necessary.

Why Duplicate or Overlapping Indexes Are a Problem

Duplicate indexes occur when two or more indexes on the same table contain exactly the same columns in the same order. Overlapping indexes, on the other hand, share the same leading key columns but may differ slightly in included columns or in the order of the remaining columns.

Problems Caused by Overlapping Indexes

  • Performance Overhead: Every data modification (INSERT, UPDATE, DELETE) must update all of these indexes, leading to increased I/O and CPU usage.
  • Query Optimizer Confusion: SQL Server’s query optimizer has more indexes to evaluate when generating execution plans, which can lead to inefficient query execution.
  • Wasted Resources: Maintaining multiple redundant indexes wastes valuable storage and processing power without providing additional benefits.

Suggested Actions

  • Drop Identical Indexes: Redundant indexes that are completely identical should be dropped to reduce overhead.
  • Merge Overlapping Indexes: For overlapping indexes, create one index that combines the necessary columns from both to reduce redundancy and improve performance.

How to Drop a Duplicate or Overlapping Index

To remove a duplicate or overlapping index, use the following SQL command:

DROP INDEX IX_Name ON TableName;
GO

Be sure to carefully review your index usage and ensure that the index isn’t required for specific queries or scenarios before dropping it.

How Aireforge Handles Duplicate or Overlapping Indexes

Aireforge automatically identifies duplicate and overlapping indexes and provides recommendations to optimize your database by either dropping or merging these indexes, depending on the level of redundancy.

Duplicate Indexes

When two indexes are exact duplicates, Aireforge recommends dropping one to avoid unnecessary maintenance and overhead.

Overlapping Indexes

If indexes share the same key columns but differ in non-key columns, Aireforge suggests merging the indexes to create a single, more efficient index. Aireforge will propose a merged index that combines the necessary key columns and included columns, allowing you to reduce redundancy while maintaining performance.

Potential Storage Savings

When Aireforge detects overlapping indexes, it also calculates the potential storage savings from dropping redundant indexes. Removing overlapping indexes not only improves query performance but also reduces the database’s overall storage footprint, which can lead to cost savings.