Category: Wait Types

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: WRITELOG Wait TypeRelated pillar: Performance & Troubleshooting Three sleep waits measure phases of instance startup, and this page covers them together: They fire once per startup and then go quiet until the next one. Are They a Problem? Not as waits;…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: ASYNC_NETWORK_IO Wait TypeRelated pillar: Performance & Troubleshooting SNI_CRITICAL_SECTION is recorded when a thread waits for a critical section inside the SQL Server Network Interface (SNI), the layer that encapsulates TDS packets and talks to clients over the configured transports. Processing communication…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: ASYNC_NETWORK_IO Wait TypeRelated pillar: Performance & Troubleshooting SNI_TASK_COMPLETION is recorded when a thread waits for tasks to finish during a NUMA node state change, specifically around creating a new SNI network listener after a NUMA node comes online. SQL Server distributes…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting SOS_DISPATCHER_MUTEX is recorded when a thread waits for the critical section inside the generic dispatcher-pool management code, including when a pool is being adjusted (grown or shrunk). Dispatcher pools are the special-purpose thread pools…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: RESOURCE_SEMAPHORE Wait TypeRelated pillar: Performance & Troubleshooting SOS_MEMORY_TOPLEVELBLOCKALLOCATOR is recorded when a thread waits for the critical section inside the memory allocator that steals memory from the buffer pool, the path used when components need large memory blocks that come out…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: RESOURCE_SEMAPHORE Wait TypeRelated pillar: Performance & Troubleshooting SOS_PHYS_PAGE_CACHE is a wait on the mutex a thread must hold before allocating physical memory pages from Windows or returning them. It shows up on instances using locked pages in memory, that is, when…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting SOS_SYNC_TASK_ENQUEUE_EVENT is recorded when a task is started synchronously: the starting thread enqueues the task on an SOS node and waits for it to actually begin running (or for the enqueue to time out).…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting SOS_WORK_DISPATCHER is recorded by a SQLOS worker thread that has become idle and is waiting to be handed something to do. The wait starts when the thread runs out of work and ends when…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting SOS_WORKER_MIGRATION appears to track a worker (thread) being moved to a different scheduler. It arrived with SQL Server 2019’s scheduling improvements, which allow a worker at the head of one scheduler’s runnable queue to…