Category: Wait Types

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability PREEMPTIVE_HADR_LEASE_MECHANISM is recorded when a thread switches to preemptive mode to renew the lease between the failover cluster and the SQL Server resource DLL, following a lease timeout. The lease is the AG’s dead-man switch:…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: ASYNC_NETWORK_IO Wait TypeRelated pillar: Performance & Troubleshooting PREEMPTIVE_OLEDBOPS is recorded when a thread switches to preemptive mode (outside SQL Server’s cooperative scheduler) to communicate with an OLE DB provider. It is the third member of the linked server wait family: OLEDB…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting A cluster of preemptive waits track Windows group membership and directory queries, and this page covers them together: PREEMPTIVE_OS_NETGROUPGETUSERS, NETLOCALGROUPGETMEMBERS, NETUSERGETGROUPS, NETUSERGETLOCALGROUPS, NETUSERMODALSGET, DOMAINSERVICESOPS, and DIRSVC_NETWORKOPS. They fire when SQL Server asks Windows who…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting PREEMPTIVE_OS_AUTHENTICATIONOPS is recorded when a thread calls Windows security functions for authentication and authorisation work: validating logins, checking group memberships, building security tokens. The thread runs preemptively (outside SQL Server’s scheduler, state showing RUNNING)…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: Performance & Troubleshooting Two preemptive waits track Windows Server Failover Clustering API calls, and this page covers both: PREEMPTIVE_OS_CLUSTEROPS (the generic bucket for cluster operations) and PREEMPTIVE_CLUSAPI_CLUSTERRESOURCECONTROL (calls to the cluster resource control API, querying and manipulating…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting PREEMPTIVE_OS_CREATEFILE is recorded while a thread calls the Windows CreateFile function. The name misleads slightly: CreateFile is Windows’ general-purpose file open API, used for reading existing files as much as creating new ones. Any…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting PREEMPTIVE_OS_DSGETDCNAME is recorded when a thread calls the Windows DsGetDcName function, which locates a domain controller for a given domain. It is the discovery step that precedes much authentication work: before validating a login…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting A large family of PREEMPTIVE_OS_* waits each track a single Windows file API call. They share one mechanic, the thread leaves SQL Server’s cooperative scheduler (state shows RUNNING) until Windows returns, and one diagnosis,…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting PREEMPTIVE_OS_FILEOPS is a generic wait covering a family of Windows file system functions that do not have their own dedicated preemptive wait type. When a thread calls one of them, it switches from SQL…

⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: WRITELOG Wait TypeRelated pillar: Performance & Troubleshooting PREEMPTIVE_OS_FLUSHFILEBUFFERS is recorded while a thread calls the Windows FlushFileBuffers function (or its equivalent on Linux), which forces everything buffered for a file down to durable media. Like all preemptive waits, the thread runs…