Why You Need to Defragment Your SQL Server Indexes

In the quest for optimal database performance, DBAs need to leave no stone unturned. After keeping the data resources in their systems secure, there is probably no task more important than providing acceptable response time to database users. A failure to keep databases performing smoothly will inevitably lead to a rash of emails and phone calls from disgruntled users and perhaps a visit from one of those management types that you strive to avoid.

One of the things that can be slowing down your SQL Server databases resulting in excessive contact with dissatisfied users is the problem of index fragmentation. Over time there is a very good chance that database indexes may become fragmented and this issue can cause a variety of performance problems. If you are an SQL Server DBA who is searching for a way to speed up your systems’ response times, defragmenting the indexes may be just what they need.

What is SQL Server Index Fragmentation?

Fragmentation is a term used to describe storing data non-contiguously on disk. Index fragmentation has been a problem since the early days of SQL Server and promises to remain with us for the foreseeable future due to the design and architecture of the database. There are two different types of index fragmentation.

  • Internal fragmentation occurs when records are not stored contiguously inside an SQL Server storage page. Over time, modifying the data with INSERT, DELETE, and UPDATE statements results in gaps and unused space between records. The unused space can cause additional I/O operations and poor cache utilization that can adversely impact query performance.

  • External fragmentation is when the logical order of pages does not coincide with their physical order on disk. This affects query execution time by necessitating more random disk reads to locate the data required to fulfill a query.

Both types of fragmentation are unavoidable in any SQL Server database that is not a static information repository. In a dynamic database that is frequently modified, fragmentation can become a recurring problem.

Effects of Fragmented Indexes

Fragmented indexes can impact your SQL Server environment in several ways that can put a strain on physical resources and degrade performance.

  • More memory will be needed to store pages while they are in use.
  • More disk space will be required on the SQL Server to store data.
  • Backup files will be larger and take longer to generate and consume more storage space.
  • Excessive disk reads and I/O operations will slow down query execution.

One specific way that index fragmentation causes slower responses is its influence on SQL Server’s query optimizer. Index fragmentation leads to indexes having more pages and are therefore identified as having a higher execution plan cost. A fragmented index can result in the index not being used as intended.

Simply implementing regularly scheduled defragmentation tasks may sound like a good idea, but can result in a lot of extra cycles and downtime for your systems. Indexes need to be monitored and addressed when fragmentation becomes a problem.

Automating the Defragmentation Process

A typical DBA has numerous tasks and activities that need to be performed on a daily, weekly, monthly, or ad hoc basis. The ability to automate some of these responsibilities can be a major factor in improving both team productivity and morale. With the right software tools, it is possible to reduce the need for manual intervention, streamline internal processes, and provide better SQL Server performance.

IDERA’s SQL Defrag Manager is the right tool for the job of keeping SQL Server index fragmentation under control across your entire environment. The application supports and reports on all SQL Server instances on-premises or in the cloud from a unified dashboard. Your database team can implement policies to perform automated defragmentation according to enterprise standards.

SQL Defrag Manager enables database teams to be more productive while eliminating one source of potential performance problems. Email alerts can be tailored to inform the staff when fragmentation is necessary and when the process is complete. It’s a tool that simplifies the management of SQL Server indexes across your organization.

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