Tuesday, 24 September 2019

wait types

http://rusanu.com/2014/02/24/how-to-analyse-sql-server-performance/#wait_info_current
====================
sys.dm_os_wait_stats-->shows the time for waits that have completed. This dynamic management view does not show current waits.

DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);--> 
GO

SELECT *
FROM sys.dm_os_wait_stats WHERE waiting_tasks_count > 0
ORDER BY wait_time_ms DESC
GO

=============================================
select session_id,
status,
command,
blocking_session_id,
wait_type,
wait_time,
last_wait_type,
wait_resource
from sys.dm_exec_requests
where r.session_id >= 50
and r.session_id <> @@spid;
==========================================================
The picture tells us what wait types are most prevalent, on aggregate, on this SQL Server instance.
This can be an important step toward identifying a bottleneck cause.

select *
from sys.dm_os_wait_stats
WHERE [wait_type] NOT IN (
        N'CLR_SEMAPHORE',    N'LAZYWRITER_SLEEP',
        N'RESOURCE_QUEUE',   N'SQLTRACE_BUFFER_FLUSH',
        N'SLEEP_TASK',       N'SLEEP_SYSTEMTASK',
        N'WAITFOR',          N'HADR_FILESTREAM_IOMGR_IOCOMPLETION',
        N'CHECKPOINT_QUEUE', N'REQUEST_FOR_DEADLOCK_SEARCH',
        N'XE_TIMER_EVENT',   N'XE_DISPATCHER_JOIN',
        N'LOGMGR_QUEUE',     N'FT_IFTS_SCHEDULER_IDLE_WAIT',
        N'BROKER_TASK_STOP', N'CLR_MANUAL_EVENT',
        N'CLR_AUTO_EVENT',   N'DISPATCHER_QUEUE_SEMAPHORE',
        N'TRACEWRITE',       N'XE_DISPATCHER_WAIT',
        N'BROKER_TO_FLUSH',  N'BROKER_EVENTHANDLER',
        N'FT_IFTSHC_MUTEX',  N'SQLTRACE_INCREMENTAL_FLUSH_SLEEP',
        N'DIRTY_PAGE_POLL',  N'SP_SERVER_DIAGNOSTICS_SLEEP')
order by wait_time_ms desc;
============================================================
To show sys.dm_os_waiting_tasks, which is a SQL Server DMV specifically designed to show currently waiting tasks:


select * from sys.dm_os_waiting_tasks
where r.session_id >= 50
and r.session_id <> @@spid;
================================================================

select r.session_id,
status,
command,
r.blocking_session_id,
r.wait_type as [request_wait_type],
r.wait_time as [request_wait_time],
t.wait_type as [task_wait_type],
t.wait_duration_ms as [task_wait_time],
t.blocking_session_id,
t.resource_description
from sys.dm_exec_requests r
left join sys.dm_os_waiting_tasks t
on r.session_id = t.session_id
where r.session_id >= 50
and r.session_id <> @@spid;
=================================================================================================================================
In order to get details of currently running queries using sys.dm_exec_requests, the following query can be used:

SELECT
 sprc.loginame as LoginName,
 db_name(sprc.dbid) DatabaseName,
 sprc.spid as SPID,
 sprc.sql_handle as SqlHandle,
CONVERT(smallint, sprc.waittype) WaitType,
 sprc.lastwaittype as WaitTypeName,
 sprc.ecid as Ecid,
 sprc.waittime as WaitTime,
req.statement_start_offset as StmOffsetStart,
 req.statement_end_offset as StmOffsetEnd,
 req.start_time as StartTime
FROM master..sysprocesses AS sprc WITH(NOLOCK) LEFT
 OUTER JOIN sys.dm_exec_requests req ON req.session_id = sprc.spid
WHERE
( sprc.dbid <> 0 AND
  sprc.spid >= 51 AND
  sprc.spid <> @@SPID AND
  sprc.cmd  <>'AWAITING COMMAND' AND
  sprc.cmd NOT LIKE '%BACKUP%' AND
  sprc.cmd NOT LIKE '%RESTORE%' AND
  sprc.hostprocess > ''
  )
=================================================================================================================================
Wait type: Logbuffer--> it is waiting for log cache to move data from logblocks.

Writelog-->(suspended) it is waiting for log cache.

Logwiter--> it is thread which is transfer the data from log cache to disk(2012 spid 1<=2012,spid 42014>=)

How to see number of outstadning i\o's?

sys.dm_io_pending_io_requests

sys.dm_io_virtual_stats-->it will gives the total stall amount of reads\writes i\o

====================
This will show the waits grouped together as a percentage of all waits on the system, in decreasing order.

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 (
        -- These wait types are almost 100% never a problem and so they are
        -- filtered out to avoid them skewing the results. Click on the URL
        -- for more information.
        N'BROKER_EVENTHANDLER', -- https://www.sqlskills.com/help/waits/BROKER_EVENTHANDLER
        N'BROKER_RECEIVE_WAITFOR', -- https://www.sqlskills.com/help/waits/BROKER_RECEIVE_WAITFOR
        N'BROKER_TASK_STOP', -- https://www.sqlskills.com/help/waits/BROKER_TASK_STOP
        N'BROKER_TO_FLUSH', -- https://www.sqlskills.com/help/waits/BROKER_TO_FLUSH
        N'BROKER_TRANSMITTER', -- https://www.sqlskills.com/help/waits/BROKER_TRANSMITTER
        N'CHECKPOINT_QUEUE', -- https://www.sqlskills.com/help/waits/CHECKPOINT_QUEUE
        N'CHKPT', -- https://www.sqlskills.com/help/waits/CHKPT
        N'CLR_AUTO_EVENT', -- https://www.sqlskills.com/help/waits/CLR_AUTO_EVENT
        N'CLR_MANUAL_EVENT', -- https://www.sqlskills.com/help/waits/CLR_MANUAL_EVENT
        N'CLR_SEMAPHORE', -- https://www.sqlskills.com/help/waits/CLR_SEMAPHORE
        N'CXCONSUMER', -- https://www.sqlskills.com/help/waits/CXCONSUMER

        -- Maybe comment these four out if you have mirroring issues
        N'DBMIRROR_DBM_EVENT', -- https://www.sqlskills.com/help/waits/DBMIRROR_DBM_EVENT
        N'DBMIRROR_EVENTS_QUEUE', -- https://www.sqlskills.com/help/waits/DBMIRROR_EVENTS_QUEUE
        N'DBMIRROR_WORKER_QUEUE', -- https://www.sqlskills.com/help/waits/DBMIRROR_WORKER_QUEUE
        N'DBMIRRORING_CMD', -- https://www.sqlskills.com/help/waits/DBMIRRORING_CMD

        N'DIRTY_PAGE_POLL', -- https://www.sqlskills.com/help/waits/DIRTY_PAGE_POLL
        N'DISPATCHER_QUEUE_SEMAPHORE', -- https://www.sqlskills.com/help/waits/DISPATCHER_QUEUE_SEMAPHORE
        N'EXECSYNC', -- https://www.sqlskills.com/help/waits/EXECSYNC
        N'FSAGENT', -- https://www.sqlskills.com/help/waits/FSAGENT
        N'FT_IFTS_SCHEDULER_IDLE_WAIT', -- https://www.sqlskills.com/help/waits/FT_IFTS_SCHEDULER_IDLE_WAIT
        N'FT_IFTSHC_MUTEX', -- https://www.sqlskills.com/help/waits/FT_IFTSHC_MUTEX

        -- Maybe comment these six out if you have AG issues
        N'HADR_CLUSAPI_CALL', -- https://www.sqlskills.com/help/waits/HADR_CLUSAPI_CALL
        N'HADR_FILESTREAM_IOMGR_IOCOMPLETION', -- https://www.sqlskills.com/help/waits/HADR_FILESTREAM_IOMGR_IOCOMPLETION
        N'HADR_LOGCAPTURE_WAIT', -- https://www.sqlskills.com/help/waits/HADR_LOGCAPTURE_WAIT
        N'HADR_NOTIFICATION_DEQUEUE', -- https://www.sqlskills.com/help/waits/HADR_NOTIFICATION_DEQUEUE
        N'HADR_TIMER_TASK', -- https://www.sqlskills.com/help/waits/HADR_TIMER_TASK
        N'HADR_WORK_QUEUE', -- https://www.sqlskills.com/help/waits/HADR_WORK_QUEUE

        N'KSOURCE_WAKEUP', -- https://www.sqlskills.com/help/waits/KSOURCE_WAKEUP
        N'LAZYWRITER_SLEEP', -- https://www.sqlskills.com/help/waits/LAZYWRITER_SLEEP
        N'LOGMGR_QUEUE', -- https://www.sqlskills.com/help/waits/LOGMGR_QUEUE
        N'MEMORY_ALLOCATION_EXT', -- https://www.sqlskills.com/help/waits/MEMORY_ALLOCATION_EXT
        N'ONDEMAND_TASK_QUEUE', -- https://www.sqlskills.com/help/waits/ONDEMAND_TASK_QUEUE
        N'PARALLEL_REDO_DRAIN_WORKER', -- https://www.sqlskills.com/help/waits/PARALLEL_REDO_DRAIN_WORKER
        N'PARALLEL_REDO_LOG_CACHE', -- https://www.sqlskills.com/help/waits/PARALLEL_REDO_LOG_CACHE
        N'PARALLEL_REDO_TRAN_LIST', -- https://www.sqlskills.com/help/waits/PARALLEL_REDO_TRAN_LIST
        N'PARALLEL_REDO_WORKER_SYNC', -- https://www.sqlskills.com/help/waits/PARALLEL_REDO_WORKER_SYNC
        N'PARALLEL_REDO_WORKER_WAIT_WORK', -- https://www.sqlskills.com/help/waits/PARALLEL_REDO_WORKER_WAIT_WORK
        N'PREEMPTIVE_XE_GETTARGETSTATE', -- https://www.sqlskills.com/help/waits/PREEMPTIVE_XE_GETTARGETSTATE
        N'PWAIT_ALL_COMPONENTS_INITIALIZED', -- https://www.sqlskills.com/help/waits/PWAIT_ALL_COMPONENTS_INITIALIZED
        N'PWAIT_DIRECTLOGCONSUMER_GETNEXT', -- https://www.sqlskills.com/help/waits/PWAIT_DIRECTLOGCONSUMER_GETNEXT
        N'QDS_PERSIST_TASK_MAIN_LOOP_SLEEP', -- https://www.sqlskills.com/help/waits/QDS_PERSIST_TASK_MAIN_LOOP_SLEEP
        N'QDS_ASYNC_QUEUE', -- https://www.sqlskills.com/help/waits/QDS_ASYNC_QUEUE
        N'QDS_CLEANUP_STALE_QUERIES_TASK_MAIN_LOOP_SLEEP',
            -- https://www.sqlskills.com/help/waits/QDS_CLEANUP_STALE_QUERIES_TASK_MAIN_LOOP_SLEEP
        N'QDS_SHUTDOWN_QUEUE', -- https://www.sqlskills.com/help/waits/QDS_SHUTDOWN_QUEUE
        N'REDO_THREAD_PENDING_WORK', -- https://www.sqlskills.com/help/waits/REDO_THREAD_PENDING_WORK
        N'REQUEST_FOR_DEADLOCK_SEARCH', -- https://www.sqlskills.com/help/waits/REQUEST_FOR_DEADLOCK_SEARCH
        N'RESOURCE_QUEUE', -- https://www.sqlskills.com/help/waits/RESOURCE_QUEUE
        N'SERVER_IDLE_CHECK', -- https://www.sqlskills.com/help/waits/SERVER_IDLE_CHECK
        N'SLEEP_BPOOL_FLUSH', -- https://www.sqlskills.com/help/waits/SLEEP_BPOOL_FLUSH
        N'SLEEP_DBSTARTUP', -- https://www.sqlskills.com/help/waits/SLEEP_DBSTARTUP
        N'SLEEP_DCOMSTARTUP', -- https://www.sqlskills.com/help/waits/SLEEP_DCOMSTARTUP
        N'SLEEP_MASTERDBREADY', -- https://www.sqlskills.com/help/waits/SLEEP_MASTERDBREADY
        N'SLEEP_MASTERMDREADY', -- https://www.sqlskills.com/help/waits/SLEEP_MASTERMDREADY
        N'SLEEP_MASTERUPGRADED', -- https://www.sqlskills.com/help/waits/SLEEP_MASTERUPGRADED
        N'SLEEP_MSDBSTARTUP', -- https://www.sqlskills.com/help/waits/SLEEP_MSDBSTARTUP
        N'SLEEP_SYSTEMTASK', -- https://www.sqlskills.com/help/waits/SLEEP_SYSTEMTASK
        N'SLEEP_TASK', -- https://www.sqlskills.com/help/waits/SLEEP_TASK
        N'SLEEP_TEMPDBSTARTUP', -- https://www.sqlskills.com/help/waits/SLEEP_TEMPDBSTARTUP
        N'SNI_HTTP_ACCEPT', -- https://www.sqlskills.com/help/waits/SNI_HTTP_ACCEPT
        N'SOS_WORK_DISPATCHER', -- https://www.sqlskills.com/help/waits/SOS_WORK_DISPATCHER
        N'SP_SERVER_DIAGNOSTICS_SLEEP', -- https://www.sqlskills.com/help/waits/SP_SERVER_DIAGNOSTICS_SLEEP
        N'SQLTRACE_BUFFER_FLUSH', -- https://www.sqlskills.com/help/waits/SQLTRACE_BUFFER_FLUSH
        N'SQLTRACE_INCREMENTAL_FLUSH_SLEEP', -- https://www.sqlskills.com/help/waits/SQLTRACE_INCREMENTAL_FLUSH_SLEEP
        N'SQLTRACE_WAIT_ENTRIES', -- https://www.sqlskills.com/help/waits/SQLTRACE_WAIT_ENTRIES
        N'WAIT_FOR_RESULTS', -- https://www.sqlskills.com/help/waits/WAIT_FOR_RESULTS
        N'WAITFOR', -- https://www.sqlskills.com/help/waits/WAITFOR
        N'WAITFOR_TASKSHUTDOWN', -- https://www.sqlskills.com/help/waits/WAITFOR_TASKSHUTDOWN
        N'WAIT_XTP_RECOVERY', -- https://www.sqlskills.com/help/waits/WAIT_XTP_RECOVERY
        N'WAIT_XTP_HOST_WAIT', -- https://www.sqlskills.com/help/waits/WAIT_XTP_HOST_WAIT
        N'WAIT_XTP_OFFLINE_CKPT_NEW_LOG', -- https://www.sqlskills.com/help/waits/WAIT_XTP_OFFLINE_CKPT_NEW_LOG
        N'WAIT_XTP_CKPT_CLOSE', -- https://www.sqlskills.com/help/waits/WAIT_XTP_CKPT_CLOSE
        N'XE_DISPATCHER_JOIN', -- https://www.sqlskills.com/help/waits/XE_DISPATCHER_JOIN
        N'XE_DISPATCHER_WAIT', -- https://www.sqlskills.com/help/waits/XE_DISPATCHER_WAIT
        N'XE_TIMER_EVENT' -- https://www.sqlskills.com/help/waits/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

======================================================================================================================

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