Performing Index Operations Online
You can create, rebuild, or drop indexes online. The ONLINE option allows concurrent user access to the underlying table or clustered index data and any associated nonclustered indexes during these index operations. For example, while a clustered index is being rebuilt by one user, that user and others can continue to update and query the underlying data. When you perform DDL operations offline, such as building or rebuilding a clustered index; these operations hold exclusive locks on the underlying data and associated indexes. This prevents modifications and queries to the underlying data until the index operation is complete.
Online index operations are available only in SQL Server Enterprise, Developer, and Evaluation editions.
We recommend performing online index operations for business environments that operate 24 hours a day, seven days a week, in which the need for concurrent user activity during index operations is vital.
The ONLINE option is available in the following Transact-SQL statements.
ALTER TABLE (To add or drop UNIQUE or PRIMARY KEY constraints with CLUSTERED index option)
In the following example, all indexes on the Product table in the AdventureWorks2008R2 sample database are rebuilt online.
USE AdventureWorks2008R2; GO ALTER INDEX ALL ON Production.Product REBUILD WITH (ONLINE = ON);