Why are we Waiting.. - DATA Idoldataidol.com/neilhambly/wp-content/uploads/sites/5/... · External waits External waits occur when a SQL Server worker is ... • User Waits DBA-320

October 11-14, Seattle, WA

Why are we Waiting..DBA-320

Neil HamblyDatabase Architect (MDSL)Founder/CTO (SQLnextSteps)

Speaker Bio: Neil Hambly

2DBA-320 | Why are we Waiting..

Permanent RolesSQLnextSteps (London) Founder/CTO - Services being launched 2012

MDSL (London) July 2010 – PresentDB Architect Editions: SQL 2005 – 2008 R2 Log-shipping, Service Broker, SSRS,SSAS

iProfile (London) Oct 2004 – June 2010DB Architect | DBA | DB Developer (Database Lead )Editions: SQL 2000 – 2005;Clustering, Service Broker, Replication, SSRS

Accenture (Dublin) June 1999– Oct 2004DBA | DB Developer (Global BI - Team Leader) Editions: SQL6.5 – 2000, Replication, DTS, OLAP

Contractor RolesBBC 14 Months (DB Support )ABN AMRO 16 Months (DB Developer )

Contact info

Neil_Hambly

http://www.linkedin.com/in/neilhambly

Email: [email protected]: http://sqlblogcasts.com/blogs/NeilHamblyUG: www.sqlserverfaq.com

London SQL Server

User Group Leader

Regular speaker &

UK SQL conferences,

regional UG events

14 years as a

SQL Professional

Background & Edition Changes

Waits & Queue Whitepaper (98 pg.) Nov 2006Author: Tom Davidson Updated: Danny Tambs, Reviewer: Sanjay Mishra

Methodology introduced and used to establish

SQL Version No of different Wait Types in edition{sys.dm_os_wait_stats} VIEW SERVER STATE permission is required to query the DMV

2000 : DBCC SQLPERF(waitstats) Still usable but does not provide max_wait_time_ms

2005 : 202 9.0.xx or 251 when used with DBCC TRACEON(8001, -1)

2008 : 484 10.0.xx includes 190 Preemptive wait_types

2008 R2 : 490 10.50.xx

Denali CTP3: 631 11.0.xx {Most of the new ones, are for new HADR functionality}


Different types of WaitsResource waitsResource waits occur when a worker requests access to a resource that is not available because the resource is being used by some other worker or is not yet available. Examples of resource waits are locks, latches, network and disk I/O waits. Lock and latch waits are waits on synchronization objects

Queue waitsQueue waits occur when a worker is idle, waiting for work to be assigned. Queue waits are most typically seen with system background tasks such as the deadlock monitor and deleted record clean-up tasks. These tasks will wait for work requests to be placed into a work queue.

External waitsExternal waits occur when a SQL Server worker is waiting for an external event, such as an extended stored procedure call or a linked server query, to finish. When you diagnose blocking issues, remember that external waits do not always imply that the worker is idle, because the worker may actively be running some external code.

Wait Categories• Backup

• Buffer I/O

• Buffer Latch

• Compilation

• CPU

• Full Text Search

• Idle

• Latch

• Lock

• Logging

• Memory

• Network I/O

• Other

• Parallelism

• SQLCLR

• Transaction

• User Waits


Note:Data Collector has categorized265 common Wait_types into these 17 Categories

Information Sources

Queues {Not covered in this session}

• Perfmon counters

Waits (DMV’s SQL 2005 & higher)Historical Waits

• sys.dm_os_wait_stats

Clear current values

DBCC SQLPERF(‘sys.dm_os_wait_stats’,CLEAR)Current Wait List

• sys.dm_os_waiting_tasksCurrent Runnable Queue

• sys.dm_exec_requests

Other Resources• Extended Events

• Datacollector

• Performance Dashboard

SQL 2000 (Before DMV’s)

DBCC SQLPERF(waitstats)


Anatomy of the DMV sys.dm_os_wait_stats

Column name Data type Description

wait_type nvarchar(60) Name of the wait type.

waiting_tasks_count bigint

Number of waits on this wait type.

This counter is incremented at the

start of each wait.

wait_time_ms bigint

Total wait time for this wait type in

milliseconds. This time is inclusive of

signal_wait_time_ms.

max_wait_time_ms bigintMaximum wait time on this wait

type.

signal_wait_time_ms bigint

Difference between the time that

the waiting thread was signalled

and when it started running.


Identify the in a Waiting State


A thread can be put in a waiting state if a required

resource is not immediately available .

Once the resource is available, thread is moved onto

the Runnable Queue and the time that it then takes

to traverse up this Queue to become active

“Running” is known as “Signal Time”

Minimising time spent not “Running” is key to an

efficient SQL Server system, thus by knowing the %

spent in a “waiting state” is critical important, it can

help us determine and overcome any potential

“resource bottlenecks” hindering overall peak

performance levels

Let’s look @ an example on our next slide

Signal Waits{now just waiting on CPU}

Waiting on another resource – IO, Locks, Network, Memory etc..

Images below from Waits & Queues Whitepaper

Current Wait List: sys.dm_os_waiting_tasks

Current Runnable Queue: sys.dm_exec_requests


Interpreting those Wait StatsWatching for / finding these

Parallelism: CXPACKET

Buffer: PAGEIOLATCH_X; PAGEIOLATCH_X

Non-Buffer: LATCH_X

I/O Issues: ASYNC_IO_COMPLETION; IO_COMPLETION,

CPU: SOS_SCHEDULER_YIELD

Trans log (Disk): WRITELOG & LOGBUFFER

Blocking: LCK_X; LCK_M_U; LCK_M_X

Memory: RESOURCE_SEMAPHORE

External: PREEMPTIVE_xxx

Backup: DISKIO_SUSPEND

SQLOS: THREADPOOL

Linked Servers: OLEDB

DBA-320 | Why are we Waiting.. 9

Some Background Waits to ignore

WHERE Wait_type NOT IN('BROKER_EVENTHANDLER','BROKER_RECEIVE_WAITFOR','BROKER_TASK_STOP','BROKER_TO_FLUSH','BROKER_TRANSMITTER','CHECKPOINT_QUEUE','CHKPT','CLR_AUTO_EVENT','CLR_MANUAL_EVENT','CLR_SEMAPHORE','DISPATCHER_QUEUE_SEMAPHORE','FT_IFTS_SCHEDULER_IDLE_WAIT','FT_IFTSHC_MUTEX','KSOURCE_WAKEUP','LAZYWRITER_SLEEP','LOGMGR_QUEUE','ONDEMAND_TASK_QUEUE','REQUEST_FOR_DEADLOCK_SEARCH','RESOURCE_QUEUE','SERVER_IDLE_CHECK','SLEEP','SLEEP_BPOOL_FLUSH','SLEEP_DBSTARTUP','SLEEP_DCOMSTARTUP','SLEEP_MSDBSTARTUP','SLEEP_SYSTEMTASK','SLEEP_TASK','SLEEP_TEMPDBSTARTUP','SNI_HTTP_ACCEPT','SQLTRACE_BUFFER_FLUSH','SQLTRACE_INCREMENTAL_FLUSH_SLEEP','Total','TRACEWRITE,WAIT_FOR_RESULTS','WAITFOR','WAITFOR_TASKSHUTDOWN','XE_DISPATCHER_JOIN'

,'XE_DISPATCHER_WAIT','XE_TIMER_EVENT')

Wait_types we can ignore #1(system & background “Queue-waits”)

DBA-320 | Why are we Waiting.. 10

Demo Time


Waits Demos in SSMS (Denali CTP3) & run following demo’s

#1 sp_whoisactive

#2 Extended events (Query results using XQuery)

#3 DataCollector

Response Time Analysis using Extended Events

Best way to illustrate this is to run a demo

For this demo I’m using a codeplex example

http://sqlcat.codeplex.com


Questions

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Titles are set 36 Century Gothic, maximum 2 lines, ideally 1 line

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October 11-14, Seattle, WA

Thank youfor attending this session and the

2011 PASS Summit in Seattle


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Documents

Why are we Waiting.. - DATA Idoldataidol.com/neilhambly/wp-content/uploads/sites/5/... · External waits External waits occur when a SQL Server worker is ... • User Waits DBA-320