Analyzing Index Usage in SQL Server

sys.dm_db_index_usage_stats is a DMV in SQL Server that returns information about how indexes are being used. It provides statistics about index usage, such as how often they are scanned, seeked, or updated, which can help in determining whether indexes are beneficial or if they need to be optimized.

Key Columns:

• database_id: ID of the database where the index is located.
• object_id: ID of the table or view that contains the index.
• index_id: ID of the index being referenced.
• user_seeks: Number of times the index was used in an index seek operation (indicating efficient use).
• user_scans: Number of times the index was used in an index scan operation.
• user_lookups: Number of times the index was used in a lookup operation (for non-clustered indexes).
• user_updates: Number of times the index was updated (indicating write operations that affect the index).
• last_user_seek: The last time the index was used in an index seek.
• last_user_scan: The last time the index was used in a scan.
• last_user_update: The last time the index was updated.

Use Case:

• You can use this DMV to identify underutilized indexes that may not be used frequently or may not provide performance benefits.
• It can help in identifying heavily scanned or updated indexes that may need optimization or restructuring.

Example Query:

SELECT 
    db_name(ius.database_id) AS database_name,
    o.name AS table_name,
    i.name AS index_name,
    ius.user_seeks,
    ius.user_scans,
    ius.user_lookups,
    ius.user_updates,
    ius.last_user_seek,
    ius.last_user_scan,
    ius.last_user_update
FROM sys.dm_db_index_usage_stats AS ius
JOIN sys.indexes AS i
    ON i.object_id = ius.object_id 
    AND i.index_id = ius.index_id
JOIN sys.objects AS o
    ON i.object_id = o.object_id
WHERE ius.database_id = DB_ID() -- Current database
ORDER BY ius.user_seeks DESC;

Explanation:

• This query retrieves the table and index names along with the counts for how often the index was used in seeks, scans, lookups, and updates.
• The ORDER BY ius.user_seeks DESC ensures that the indexes that are most frequently sought are listed first.
• The query also includes timestamps of when the index was last used in these operations.