Parallel Queries

Microsoft SQL Server 7.0 introduces intra-query parallelism, which is the ability to break a single query into multiple subtasks and execute them on multiple processors in an SMP computer.

SQL Server accomplishes this by automatically detecting that it is running on an SMP computer and determining the best degree of parallelism for each instance of a parallel query execution. By examining the current system workload and configuration, SQL Server determines the optimal number of threads and spreads the parallel query execution across those threads. When a query starts executing, it uses the same number of threads until completion. SQL Server chooses the optimal number of threads each time a parallel query execution plan is retrieved from the procedure cache. As a result, one execution of a query can use a single thread, and another execution of the same query (at a different time) can use two or more threads.

In addition to parallel queries, Microsoft SQL Server 7.0 supports parallel backup, parallel restore, and parallel load using multiple clients. For more information, see SQL Server Books Online.