How to Identify and Resolve SQL Server Index Fragmentation April 16, 2025

This article will explain how to identify and resolve SQL Server index fragmentation, which is important for maintaining database performance and ensuring efficient query execution.

Here’s how to identify and resolve SQL Server Index fragmentation:

1. Identifying Index Fragmentation
   With the comprehensive statistics on fragmentation levels, the sys.dm_db_index_physical_stats DMV makes it simple to monitor index fragmentation in SQL Server. A brief query to verify fragmentation is as follows:

   SELECT 
   
       dbschemas.[name] AS ‘Schema’,
   
       dbtables.[name] AS ‘Table’,
   
       dbindexes.[name] AS ‘Index’,
   
       indexstats.avg_fragmentation_in_percent
   
   FROM 
   
       sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, ‘LIMITED’)
   
   indexstats
   
       INNER JOIN sys.objects dbtables ON indexstats.object_id = dbtables.object_id
   
       INNER JOIN sys.schemas dbschemas ON dbtables.schema_id =
   
   dbschemas.schema_id
   
       INNER JOIN sys.indexes dbindexes ON dbtables.object_id = dbindexes.object_id
   
   WHERE 
   
       indexstats.avg_fragmentation_in_percent > 10
   
   ORDER BY 
   
       indexstats.avg_fragmentation_in_percent DESC;

   You can use this query to determine whether to rebuild or rearrange your most fragmented indexes.

2. Fixing SQL Server Index Fragmentation
   There are two methods for repairing fractured indexes once you’ve found them:
   1. Rebuild the Index
      1. When to Use: Suggested for high fragmentation (above 30%).
      2. Process: This method completely removes fragmentation by dropping and recreating the index. It is faster but resource-intensive.
      3. Command:

         ALTER INDEX [YourIndexName] ON [dbo].[YourTableName] REBUILD;

   2. Reorganise the Index
      1. When to Use: Best for low fragmentation (under 30%).
      2. Process: This method defragments the index without rebuilding it from scratch, using fewer resources but taking longer.
      3. Command:
         ALTER INDEX [YourIndexName] ON [dbo].[YourTableName] REORGANISE;
         Main Difference: While reorganising is less resource-intensive but takes longer, rebuilding is quicker but uses more system resources.
   3. Maintaining Your SQL Server Index
      1. Update Statistics: After rebuilding or reorganising your indexes, it’s crucial to update the statistics that SQL Server uses to optimise queries. Outdated statistics can lead to suboptimal execution plans, even if the indexes are defragmented.

         UPDATE STATISTICS [dbo].[YourTableName] WITH FULLSCAN;

      2. Automate Index Maintenance: Regular index maintenance is vital to avoid performance degradation. You can automate this process using SQL Server Agent to schedule index rebuilds or reorganisations during off-peak hours. This ensures that your database remains optimised without manual intervention.

This way, you can identify and resolve SQL server index fragmentation. However, if you need assistance, feel free to contact our support staff at your earliest.

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