Cleaning Up Unused Indexes Without Breaking Performance
Indexes tend to outlive the problems that created them. It usually starts with a slow query. An engineer adds an index, the immediate issue goes away, and everyone moves on. At the time, the decision makes sense. The problem is that the index often stays in place long after the application changes, a report is replaced, or a feature quietly falls out of use. Over time, a busy table can collect a…
Unused indexes can accumulate over time and cause performance issues, even if they are no longer needed. They may remain in place for various reasons, such as an outdated query, a feature that is temporarily disabled, or a scheduled report. To address this issue, DBAs can use the sys.dm_db_index_usage_stats DMV to analyze index usage patterns and identify candidates for review or deletion.
To perform this analysis, start by building a baseline inventory of indexes in the database. This script retrieves usage statistics, index size, and basic metadata for rowstore indexes that are not hypothetical, primary keys, or unique. The results are grouped by schema, table, and index name, with columns for index type, size in MB, and the number of reads, writes, and updates.
When evaluating unused indexes, consider factors such as index size, update frequency, and the importance of the workload that may still rely on the index. A zero reading counter does not necessarily mean an index is unnecessary; it may still be useful for specific jobs, quarterly reports, or disaster recovery exercises. As such, DBAs should avoid deleting indexes based on a single snapshot and instead gradually remove indexes after thorough evaluation and monitoring of their impact on the workload.
To ensure accurate results, the script collects data over a sufficient period to capture the workload's history, even if SQL Server restarts or the database is shut down. This approach allows DBAs to make informed decisions when deciding which indexes to remove, minimizing the risk of unintended performance degradation.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
