Data World

MSSSQL Server Tuning – Find Wait stats

Posted by Pramod Singla on March 5, 2017


Problem Statement: Script to get the SQL Server wait stats. You can find the significance of most common waits below it.
Solution: Knowing resource waits is the good way to start the performance tuning.Following is the good script i got from SQL skills.

WITH [Waits]
AS (SELECT [wait_type],
[wait_time_ms] / 1000.0                             AS [WaitS],
( [wait_time_ms]  [signal_wait_time_ms] ) / 1000.0 AS
[ResourceS],
[signal_wait_time_ms] / 1000.0                      AS [SignalS]
,
[waiting_tasks_count]
AS [WaitCount],
100.0 * [wait_time_ms] / Sum ([wait_time_ms])
OVER()                   AS
[Percentage],
ROW_NUMBER()
OVER(
ORDER BY [wait_time_ms] DESC)                   AS [RowNum]
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’,
— Maybe uncomment these four if you have mirroring issues
N’DBMIRROR_DBM_EVENT’, 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’,
— Maybe uncomment these six if you have AG issues
N’HADR_CLUSAPI_CALL’,

,
N’HADR_LOGCAPTURE_WAIT’,
N’HADR_NOTIFICATION_DEQUEUE’,
N’HADR_TIMER_TASK’, N’HADR_WORK_QUEUE’,
N’KSOURCE_WAKEUP’,
N’LAZYWRITER_SLEEP’
,
N’LOGMGR_QUEUE’, N’MEMORY_ALLOCATION_EXT’,
N’ONDEMAND_TASK_QUEUE’,
N’PREEMPTIVE_XE_GETTARGETSTATE’,
N’PWAIT_ALL_COMPONENTS_INITIALIZED’,
N’PWAIT_DIRECTLOGCONSUMER_GETNEXT’,
N’QDS_PERSIST_TASK_MAIN_LOOP_SLEEP’
,
N’QDS_ASYNC_QUEUE’,
N’QDS_CLEANUP_STALE_QUERIES_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’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’WAIT_FOR_RESULTS’,
N’WAITFOR’,
N’WAITFOR_TASKSHUTDOWN’,
N’WAIT_XTP_RECOVERY’, N’WAIT_XTP_HOST_WAIT’,
N’WAIT_XTP_OFFLINE_CKPT_NEW_LOG’,
N’WAIT_XTP_CKPT_CLOSE’,
N’XE_DISPATCHER_JOIN’, N’XE_DISPATCHER_WAIT’,
N’XE_TIMER_EVENT’ )
AND [waiting_tasks_count] > 0)
SELECT Max ([W1].[wait_type])
AS
[WaitType],
Cast (Max ([W1].[WaitS]) AS DECIMAL (16, 2))
AS [Wait_S],
Cast (Max ([W1].[ResourceS]) AS DECIMAL (16, 2))
AS [Resource_S],
Cast (Max ([W1].[SignalS]) AS DECIMAL (16, 2))
AS [Signal_S],
Max ([W1].[WaitCount])
AS [WaitCount],
Cast (Max ([W1].[Percentage]) AS DECIMAL (5, 2))
AS [Percentage],
Cast (( Max ([W1].[WaitS]) / Max ([W1].[WaitCount]) ) AS DECIMAL (16, 4))
AS
[AvgWait_S],
Cast (( Max ([W1].[ResourceS]) / Max ([W1].[WaitCount]) ) AS
DECIMAL (16, 4)) AS
[AvgRes_S],
Cast (( Max ([W1].[SignalS]) / Max ([W1].[WaitCount]) ) AS
DECIMAL (16, 4))   AS
[AvgSig_S],
Cast (https://www.sqlskills.com/help/waits/’
+ Max ([W1].[wait_type]) AS XML)
AS [Help/Info URL]
FROM   [Waits] AS [W1]
INNER JOIN [Waits] AS [W2]
ON [W2].[RowNum] <= [W1].[RowNum]
GROUP  BY [W1].[RowNum]
HAVING Sum ([W2].[Percentage])  Max([W1].[Percentage]) < 95; — percentage threshold

GO

Common Significant Wait types explanations are as:

Sno. Wait Type Description
1. LCK_M_IX Occurs when a task is waiting to acquire an Intent Exclusive (IX) lock
2. LCK_M_IU Occurs when a task is waiting to acquire an Intent Update (IU) lock
3. LCK_M_S Occurs when a task is waiting to acquire a Shared lock
4. ASYNC_NETWORK_IO Occurs on network writes when the task is blocked behind the network
5. ASYNC_IO_COMPLETION Occurs when a task is waiting for I/Os to finish
6.  

IO_COMPLETION

Occurs while waiting for I/O operations to complete.                       This wait type generally represents non-data page I/Os. Data page I/O completion waits appear
7. PAGEIOLATCH_SH Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem.
8.  

 

PAGEIOLATCH_EX

 

Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem.

 

9. WRITELOG

 

Occurs while waiting for a log flush to complete.Common operations that cause log flushes are checkpoints and transaction commits.
10. PAGELATCH_EX

 

Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Exclusive mode.
11. BACKUPIO

 

Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data
12. SOS_SCHEDULER_YIELD

 

Occurs when a task voluntarily yields the scheduler for other tasks to execute.  During this wait the task is waiting for its quantum to be renewed.
13. THREADPOOL

 

Occurs when a task is waiting for a worker to run on. This can indicate that the maximum worker setting is too low, or that batch executions are taking  unusually long, thus reducing the number of workers available to satisfy other batches.
14. CX_PACKET

 

Occurs when trying to synchronize the query processor exchange iterator
15. ONDEMAND_TASK_QUEUE

 

Occurs while a background task waits for high priority system task requests. Long wait times indicate that there have been no high priority requests to process, and should not cause concern. You may consider lowering the degree of parallelism if contention on this wait type becomes a problem
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One Response to “MSSSQL Server Tuning – Find Wait stats”

  1. […] MSSSQL Server Tuning – Find Wait stats […]

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