What do you do when your server is slow? How do you find out the bottlenecks on the SQL server? SQL server has a bunch of DMVs that you can query to check what SQL server is waiting on. These are called Wait Statistics, aka Wait Stats.
Types of Waits
1. Resource waits such as locks, latches, network and disk I/O waits
2. Queue waits occur when a worker is idle, waiting for work to be assigned. Typically system background tasks such as the deadlock monitor and deleted record cleanup tasks.
3. External waits such as an extended stored procedure call or a linked server query
Here is a handy little query courtesy of Pinal Dave:
/*
-- Script to Clear Wait Types
DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR);
GO
*/
SELECT wait_type AS Wait_Type,
wait_time_ms / 1000.0 AS Wait_Time_Seconds,
waiting_tasks_count AS Waiting_Tasks_Count,
-- CAST((wait_time_ms / 1000.0)/waiting_tasks_count AS decimal(10,4)) AS AVG_Waiting_Tasks_Count,
wait_time_ms * 100.0 / SUM(wait_time_ms) OVER() AS Percentage_WaitTime
--,waiting_tasks_count * 100.0 / SUM(waiting_tasks_count) OVER() AS Percentage_Count
FROM sys.dm_os_wait_stats
WHERE wait_type NOT IN
(N'BROKER_EVENTHANDLER',
N'BROKER_RECEIVE_WAITFOR',
N'BROKER_TASK_STOP',
N'BROKER_TO_FLUSH',
N'BROKER_TRANSMITTER',
N'CHECKPOINT_QUEUE',
N'CHKPT',
N'CLR_AUTO_EVENT',
N'CLR_MANUAL_EVENT',
N'CLR_SEMAPHORE',
N'CXCONSUMER',
N'DBMIRROR_DBM_EVENT',
N'DBMIRROR_DBM_MUTEX',
N'DBMIRROR_EVENTS_QUEUE',
N'DBMIRROR_WORKER_QUEUE',
N'DBMIRRORING_CMD',
N'DIRTY_PAGE_POLL',
N'DISPATCHER_QUEUE_SEMAPHORE',
N'EXECSYNC',
N'FSAGENT',
N'FT_IFTS_SCHEDULER_IDLE_WAIT',
N'FT_IFTSHC_MUTEX',
N'HADR_CLUSAPI_CALL',
N'HADR_FILESTREAM_IOMGR_IOCOMPLETION',
N'HADR_LOGCAPTURE_WAIT',
N'HADR_NOTIFICATION_DEQUEUE',
N'HADR_TIMER_TASK',
N'HADR_WORK_QUEUE',
N'LAZYWRITER_SLEEP',
N'LOGMGR_QUEUE',
N'MEMORY_ALLOCATION_EXT',
N'ONDEMAND_TASK_QUEUE',
N'PARALLEL_REDO_DRAIN_WORKER',
N'PARALLEL_REDO_LOG_CACHE',
N'PARALLEL_REDO_TRAN_LIST',
N'PARALLEL_REDO_WORKER_SYNC',
N'PARALLEL_REDO_WORKER_WAIT_WORK',
N'PREEMPTIVE_HADR_LEASE_MECHANISM',
N'PREEMPTIVE_OS_FLUSHFILEBUFFERS',
N'PREEMPTIVE_OS_AUTHENTICATIONOPS',
N'PREEMPTIVE_OS_AUTHORIZATIONOPS',
N'PREEMPTIVE_OS_COMOPS',
N'PREEMPTIVE_OS_CREATEFILE',
N'PREEMPTIVE_OS_CRYPTOPS',
N'PREEMPTIVE_OS_DEVICEOPS',
N'PREEMPTIVE_OS_FILEOPS',
N'PREEMPTIVE_OS_GENERICOPS',
N'PREEMPTIVE_OS_LIBRARYOPS',
N'PREEMPTIVE_OS_PIPEOPS',
N'PREEMPTIVE_OS_QUERYREGISTRY',
N'PREEMPTIVE_OS_VERIFYTRUST',
N'PREEMPTIVE_OS_WAITFORSINGLEOBJECT',
N'PREEMPTIVE_OS_WRITEFILEGATHER',
N'PREEMPTIVE_SP_SERVER_DIAGNOSTICS',
N'PREEMPTIVE_XE_CALLBACKEXECUTE',
N'PREEMPTIVE_XE_DISPATCHER',
N'PREEMPTIVE_XE_GETTARGETSTATE',
N'PREEMPTIVE_XE_SESSIONCOMMIT',
N'PREEMPTIVE_XE_TARGETFINALIZE',
N'PREEMPTIVE_XE_TARGETINIT',
N'PWAIT_ALL_COMPONENTS_INITIALIZED',
N'PWAIT_EXTENSIBILITY_CLEANUP_TASK',
N'PWAIT_DIRECTLOGCONSUMER_GETNEXT',
N'QDS_ASYNC_QUEUE',
N'QDS_CLEANUP_STALE_QUERIES_TASK_MAIN_LOOP_SLEEP',
N'QDS_PERSIST_TASK_MAIN_LOOP_SLEEP',
N'QDS_SHUTDOWN_QUEUE',
N'REDO_THREAD_PENDING_WORK',
N'REQUEST_FOR_DEADLOCK_SEARCH',
N'RESOURCE_QUEUE',
N'SERVER_IDLE_CHECK',
N'SOS_WORK_DISPATCHER',
N'SLEEP_BPOOL_FLUSH',
N'SLEEP_DBSTARTUP',
N'SLEEP_DCOMSTARTUP',
N'SLEEP_MASTERDBREADY',
N'SLEEP_MASTERMDREADY',
N'SLEEP_MASTERUPGRADED',
N'SLEEP_MSDBSTARTUP',
N'SLEEP_SYSTEMTASK',
N'SLEEP_TASK',
N'SLEEP_TEMPDBSTARTUP',
N'SNI_HTTP_ACCEPT',
N'SP_SERVER_DIAGNOSTICS_SLEEP',
N'SQLTRACE_BUFFER_FLUSH',
N'SQLTRACE_INCREMENTAL_FLUSH_SLEEP',
N'SQLTRACE_WAIT_ENTRIES',
N'STARTUP_DEPENDENCY_MANAGER',
N'UCS_SESSION_REGISTRATION',
N'VDI_CLIENT_OTHER',
N'WAIT_FOR_RESULTS',
N'WAIT_XTP_CKPT_CLOSE',
N'WAIT_XTP_HOST_WAIT',
N'WAIT_XTP_OFFLINE_CKPT_NEW_LOG',
N'WAIT_XTP_RECOVERY',
N'WAITFOR',
N'WAITFOR_TASKSHUTDOWN',
N'XE_BUFFERMGR_ALLPROCESSED_EVENT',
N'XE_DISPATCHER_JOIN',
N'XE_TIMER_EVENT',
N'XE_DISPATCHER_WAIT',
N'XE_LIVE_TARGET_TVF'
) AND wait_time_ms >= 1
ORDER BY Wait_Time_Seconds DESC
-- ORDER BY Waiting_Tasks_Count DESC
-- SQL Wait Stats and Queries
-- (C) Pinal Dave (http://blog.sqlauthority.com) 2021+
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