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Index Fragmentation in SQL Server: The Essentials

Level 12

What is Index Fragmentation?

SQL server has indexes for organizing data within the database. Having a clean index helps you perform SQL operations efficiently. When you modify or update the data in your SQL server, the index content scatter. This scatter is what’s referred to as index fragmentation.


Why does it occur?


Fragmentation occurs because of the following:

  • Adding new information to the database
  • Modifying or editing the existing database
  • Removing information from the database

Even a simple operation like inserting a new row or updating a row can create empty spaces in the database causing indexes to fragment.

How do fragmented indexes affect SQL server performance?


Highly fragmented indexes can significantly decrease database performance. When one of the following occurs, you’ll know it could be due to fragmented indexes:

  • Queries take longer to respond
  • More disk space is utilized
  • Applications take time to respond
  • Database server may be slow to respond to modifications and additions done to the database

Whatever the issue is, it’s worth looking into the database indexes to check for fragmentation.


Repair Index Fragmentation

Just because there’s going to be fragmentation when you modify the database doesn't mean that you should stop updating or modifying it. It is good to proactively monitor SQL servers to ensure index fragmentation does not affect the overall database performance. Having a clean index will ensure data searches are faster in SQL server. Whether you’re making adjustments to the database or trying to retrieve information, having a proper index will get your job done faster. You can do the following to improve performance in case of an issue:

  • Rebuild and reorganize indexes periodically.
  • Monitor query performance, this helps to avoid bottlenecks.
  • Monitor what your storage drives are doing to the database. This will help you determine if the issue has to do with your indexes or your storage system.
  • Ensure you have a regular maintenance cycle in place.

Here is something to keep in mind: Be sure your indexes are fragmented before you decide to defragment. By determining this, you’ll know what the next steps are that you can do to improve your SQL server performance. A server monitoring tool will tell you if your database indexes are fragmented along with other critical metrics to improve overall SQL server performance. With a server monitoring tool, you can also set baseline values to your database indexes. That way, you’re not only notified but you can also proactively identify and fix issues before it impacts more end users.

1 Comment
Level 15

Helpful information.