Resumable Online Index Rebuild in SQL Server

Azure SQL Database and the upcoming release of SQL Server enhance Online Index Rebuild to provide fault-tolerance and allow index rebuild operations to resume after a system failure or a userinitiated pause. SQL Server is the first commercial DBMS to support pause and resume functionality for index rebuilds. This is achieved by splitting the operation into incremental units of work and persisting the required state so that it can be resumed later with minimal loss of progress. At the same time, the proposed technology minimizes the log space required for the operation to succeed, making it possible to rebuild large indexes using only a small, constant amount of log space. These capabilities are critical to guarantee the reliability of these operations in an environment where a) the database sizes are increasing at a much faster pace compared to the available hardware, b) system failures are frequent in Cloud architectures using commodity hardware, c) software upgrades and other maintenance tasks are automatically handled by the Cloud platforms, introducing further unexpected failures for the users and d) most modern applications need to be available 24/7 and have very tight maintenance windows. This paper describes the design of “Resumable Online Index Rebuild” and discusses how this technology can be extended to cover more schema management operations in the future.