Affinity synonym1/27/2024 For more information about waiting tasks, see sys.dm_os_waiting_tasks.Ī SQL Server worker thread, also known as worker or thread, is a logical representation of an operating system thread. Tasks in SUSPENDED state are waiting on resources required to execute the task to become available. For more information about task states, see sys.dm_os_tasks. Tasks exist in various states throughout their lifetime. Serial requests only have one active task at any given point in time during execution. The parent task is also responsible for executing those serial operators. An execution plan for a parallel request may have serial branches - areas of the plan with operators that don't execute in parallel. Parallel requests have several active tasks that are executed concurrently instead of serially, with one parent task (or coordinating task) and multiple child tasks.One or more tasks can be assigned to a single request. TasksĪ task represents the unit of work that needs to be completed to fulfill the request. For more information about request states, see sys.dm_exec_requests. Requests exist in various states throughout their lifetime and can accumulate waits when resources required to execute the request aren't available, such as locks or latches. A request also represents operations required by system threads, such as checkpoint or log writer. In the scope of SQL Server, a request is the logical representation of a query or batch. For example, if a computer has eight CPUs, it can execute eight threads at the same time. Computers that have multiple CPUs can execute one thread per CPU at the same time. This is especially true for multi-user, disk I/O intensive applications such as a database server. By being able to execute threads while other threads are waiting for an operation to be completed, an application can maximize its use of the CPU. If one thread executes a long-running operation that doesn't use the CPU, such as a disk read or write, another one of the threads can execute until the first operation is completed. With one CPU, only one thread can execute at a time. Threads allow complex applications to make more effective use of a processor (CPU), even on computers that have a single CPU. Additionally, each thread can be scheduled for execution independently from the other threads associated with a process. An application can do this by starting separate processes for each task, which is a resource-intensive operation, or start separate threads, which are relatively less resource-intensive. More complex applications may have several tasks that can be performed concurrently instead of serially. For example, if a simple application has a single set of instructions that can be performed serially, that set of instructions is handled as a single task, and there is just one execution path (or thread) through the application. This is the series of programming instructions performed by the application code. When an operating system executes an instance of an application, it creates a unit called a process to manage the instance. Threads are useful when complex applications have many tasks that can be performed at the same time. Threads are the smallest units of processing that are executed by an operating system, and allow the application logic to be separated into several concurrent execution paths. Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Operating system task scheduling
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