Author: Peter Whyte
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CLR_SEMAPHORE Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting CLR_SEMAPHORE is recorded when a task executing CLR code waits to acquire a semaphore, one of the synchronisation primitives CLR threads use to gate access to limited resources. Like its sibling CLR_AUTO_EVENT, it comes…
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CLR_MANUAL_EVENT Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting CLR_MANUAL_EVENT is recorded when a task performing CLR execution waits for a manual-reset event to be signalled. In practice it is mostly CLR worker threads standing by for work, the manual-reset sibling of CLR_AUTO_EVENT,…
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DBA Scripts: Get Query Store Top Queries
🔧Part of the DBA-Tools Project, copy/paste SQL Server scripts and health checks.In: Performance & Troubleshooting › Query & Performance Tuning Query Store is SQL Server’s built-in flight recorder for query performance: every query’s plan, runtime stats, and history, retained and queryable without any extra tracing setup. Most instances have had it available since SQL Server…
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CLR_AUTO_EVENT Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting CLR_AUTO_EVENT is recorded when a task running Common Language Runtime (CLR) code waits on an auto-reset event, which in practice is mostly CLR worker threads waiting for something to do. If CLR integration is…
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ASSEMBLY_LOAD and CLR Assembly Wait Types in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting Four waits cover CLR assembly loading and task startup, and this page covers them together: Together they describe .NET code arriving and getting under way inside the engine. Are They a Problem? Rarely; none…
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CHKPT Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: IO_COMPLETION Wait TypeRelated pillar: Storage & Capacity CHKPT is recorded at instance startup while the background checkpoint process initialises and waits for the signal that it can start. It happens once per instance start, and that is the whole story: one…
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CHECKPOINT_QUEUE Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: IO_COMPLETION Wait TypeRelated pillar: Storage & Capacity CHECKPOINT_QUEUE is recorded by the background checkpoint process while it sits idle, waiting for the next checkpoint request to be placed on its queue. Between checkpoints there is nothing for it to do, so…
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CHECK_TABLES_THREAD_BARRIER Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: IO_COMPLETION Wait TypeRelated pillar: Performance & Troubleshooting CHECK_TABLES_THREAD_BARRIER is recorded when a parallel thread in a DBCC CHECKDB (or related) command waits at a barrier for its sibling threads, either while they finish initialising, or while they finish exiting after certain…
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CHECK_TABLES_INITIALIZATION Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: IO_COMPLETION Wait TypeRelated pillar: Performance & Troubleshooting CHECK_TABLES_INITIALIZATION is recorded when a parallel thread belonging to a DBCC CHECKDB (or CHECKTABLE/CHECKFILEGROUP) command initialises and has to wait on a mutex that another initialising thread currently holds. Parallel DBCC spins up a…
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BROKER_TRANSMITTER Wait Type in SQL Server
⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting BROKER_TRANSMITTER is recorded when the Service Broker transmission queue is empty and the two internal transmitter threads (the ones that send messages to remote endpoints) wait for work. Two threads waiting simultaneously gives this…
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