Script to Manage SQL Server Rebuilds and Reorganize for Index Fragmentation

By:Artemakis Artemiou || Related Tips:More > Fragmentation and Index Maintenance

Problem

Indexes are one of the main database objects in SQL Server that massively contribute towards performance. By using the proper indexes, you can avoid fully scanning millions of records in tables in order to find what you are looking for. Instead of scanning the tables, you can traverse the index tree (index seek operation) and find what you are looking for much faster.

Even though indexes are very handy and necessary in performant database designs, they need maintenance. One of the reasons for that is fragmentation. The SQL Server Database Engine automatically maintains indexes whenever insert, update or delete modifications take place. However, over time and especially when heavy data modifications take place, index data becomes scattered in the database and thus fragmented. This fragmentation affects the performance of the index seek process, because these indexes do not have the exact logical ordering with the physical ordering inside the database's data file(s).

One way to handle this issue is by rebuilding fragmented indexes. If you do this using a Maintenance Plan, you will rebuild every single index in the database instead of rebuilding only the fragmented indexes (this has changed in SQL Server 2016). This tip provides a fully parameterized T-SQL script which identifies only the fragmented indexes in a database or in all databases in a SQL Server instance, and either generates a report with the defragmentation commands for review and controlled execution, or directly reorganizes or rebuilds the fragmented indexes based on Microsoft's recommendations . The script also supports AlwaysOn AG-enabled SQL Server instances.

Solution

Before presenting the script, let's first discuss a bit about the process of rebuilding indexes. First of all, never rebuild indexes that do not need to be rebuilt. As per Microsoft's recommendation , when an index has an average fragmentation percentage (use sys.dm_db_index_physical_stats to get these stats) larger than 5% and smaller or equal to 30% you do not need to rebuild the index. In this case, you just need to reorganize it. When the index has an average fragmentation percentage over 30%, then yes, you need to rebuild it. In more modern SQL Server setups, like for example AlwaysOn Availability Groups, you must make additional checks in your index maintenance scripts. For example you must check if a database is the primary replica or not. If it is the primary replica then you can proceed with the index maintenance.

The T-SQL Script presented in this tip handles all the above. You can run it on clustered SQL Server instances, AlwaysOn Availability Group enabled instances, etc. It has built-in logic that based on Microsoft's recommendations dynamically generates reorganization or rebuild statements only for the fragmented indexes.

SQL Server Index Rebuild and Reorganize Script

The script uses the following parameters:

@reportOnly (required)

Values:

- 0: The script will reorganize or rebuild the fragmented indexes.

- 1: The script will just output the index reorganization or rebuild commands without running them.

@databaseToCheck (optional)

Values:

- NULL: It will scan all databases with compatibility level SQL Server 2005 (90) or later for fragmented indexes.

- 'DatabaseName': It will scan only the given database for fragmented indexes.

@fragmentationThreshold (required)

Description: It maintains only the indexes that have average fragmentation percentage equal or higher from the given value.

Value Range: 5-100

@indexFillFactor (required)

Description: The percentage of the data page to be filled up with index data.

Recommended Value Range: 90-100

@indexStatisticsScanningMode (required)

Description: The scanning mode for index statistics

Available Values: 'DEFAULT', NULL, 'LIMITED', 'SAMPLED', or 'DETAILED'.

Recommended Value: 'SAMPLED'

@sortInTempdb (required)

Values:

- 'ON': Sorts intermediate index results in TempDB.

- 'OFF': Sorts intermediate index results in user database's log file.

@verboseMode (optional)

Values:

0: It does not output additional information on the index reorganization/rebuild process.

1: It outputs additional information on the index reorganization/rebuild process.

Also, please note the following conditions :

You must be a SysAdmin in order to execute the script. The script supports only SQL Server 2005 or later. If you execute this script in a SQL Server 2005 instance or later, any databases with compatibility level 2000 (80) or earlier will be automatically excluded from the index reorganization/rebuild process.

The script is provided below:

----
-- Script that reorganizes or rebuilds all indexes having an average fragmentation
-- percentage above a given threshold. It also works in the case
-- where Availability Groups are enabled as it determines if the
-- relevant databases are the primary replicas.
--
-- This script supports only SQL Server 2005 or later.
-- Also, if you execute this script in a SQL Server 2005 instance
-- or later, any databases with compatibility level 2000 (80) or earlier
-- will be automatically excluded from the index reorganization/rebuild process.
----
--Initial check - You must be SysAdmin
DECLARE @isSysAdmin INT
SSET @isSysAdmin=(SELECT IS_SRVROLEMEMBER ('sysadmin'));
--Initial check - You must be using SQL Server 2005 or laterDECLARE @SQLServerVersion INT
SET @SQLServerVersion=(SELECT CAST(LEFT(CAST(SERVERPROPERTY('ProductVersion') AS VARCHAR(50)),CHARINDEX('.',CAST(SERVERPROPERTY('ProductVersion') AS VARCHAR(50)))-1) AS INT));
IF @isSysAdmin=1 AND @SQLServerVersion >= 9
BEGIN
--
-- Variable/parameters Declaration
--
DECLARE @dbname NVARCHAR(128);
DECLARE @ReorganizeOrRebuildCommand NVARCHAR(MAX);
DECLARE @dbid INT;
DECLARE @indexFillFactor VARCHAR(5);
DECLARE @fragmentationThreshold VARCHAR(10);
DECLARE @indexStatisticsScanningMode VARCHAR(20);
DECLARE @verboseMode BIT;
DECLARE @reportOnly BIT;
DECLARE @sortInTempdb VARCHAR(3);
DECLARE @isHadrEnabled BIT;
DECLARE @databaseToCheck VARCHAR(250)
DECLARE @dynamic_command NVARCHAR(1024);
DECLARE @dynamic_command_get_tables NVARCHAR(MAX);
--Initializations - Do not change
SET @databaseToCheck=NULL;
SET @dynamic_command = NULL;
SET @dynamic_command_get_tables = NULL;
SET @isHadrEnabled=0;
SET NOCOUNT ON;
---------------------------------------------------------
--Set Parameter Values: You can change these (optional) -
--Note: The script has default parameters set -
---------------------------------------------------------
--if set to 1: it will just generate a report with the index reorganization/rebuild statements
--if set to 0: it will reorganize or rebuild the fragmented indexes
SET @reportOnly = 0;
--optional: if not set (NULL), it will scan all databases
--If name is set (i.e. 'testDB') it will just scan the given database
SET @databaseToCheck = NULL;
--maintains only the indexes that have average fragmentation percentage equal or higher from the given value
SET @fragmentationThreshold = 15;
--fill factor - the percentage of the data page to be filled up with index data
SET @indexFillFactor = 90;
--sets the scanning mode for index statistics
--a