Diagnosing Performance with Wait Statistics Robert L Davis Principal Database

Robert L Davis Principal Database Architect at DB Best Technologies Greater Seattle Area | Information Technology and Services Past: Blog: Twitter: LinkedIN: Principal DBA at Outerwall, Inc. P.M. SQL Server Master Certification Program at Microsoft Sr. Database Administrator at Microsoft

Diagnosing Performance with Wait Statistics “Find the problem, FIX IT. Identify another problem, FIX IT. Repeat as necessary.” ~ Keenan Thompson (Saturday Night Live)

Diagnosing Performance with Wait Statistics  Medical approach to troubleshooting

Diagnosing Performance with Wait Statistics  Medical approach to troubleshooting  Baseline vital statistics  Performance counters  DMV stats

Diagnosing Performance with Wait Statistics  Medical approach to troubleshooting  Baseline vital statistics  Performance counters  DMV stats  Recheck vital statistics and compare

Diagnosing Performance with Wait Statistics  Medical approach to troubleshooting  Baseline vital statistics  Performance counters  DMV stats  Recheck vital statistics and compare  Find deviations from the norm

Diagnosing Performance with Wait Statistics  Medical approach to troubleshooting  Baseline vital statistics  Performance counters  DMV stats  Recheck vital statistics and compare  Find deviations from the norm  Read more:

Diagnosing Performance with Wait Statistics  Baseline for Performance

Diagnosing Performance with Wait Statistics  Baseline for Performance  Processor(*)\% Processor Time  PhysicalDisk\Avg. Disk sec/Read  PhysicalDisk\Avg. Disk sec/Write  Memory\Pages/sec  Memory\Available Bytes  SQLServer:Buffer Manager\Page life expectancy  SQLServer:GeneralStatistics\Processes Blocked  SQLServer:Access Methods\Full Scans/sec  SQLServer:SQL Statistics\Batch requests/sec  SQLServer:Buffer Manager\Lazy writes/sec  SQLServer:Buffer Manager\Buffer Cache Hit Ratio  SQLServer:Databases (*)\Transactions/sec

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  Wait statistics

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  Wait statistics  sys.dm_os_wait_stats  sys.dm_os_waiting_tasks  sys.dm_exec_requests  sys.dm_exec_sessions  sys.dm_exec_query_plan()  sys.dm_exec_sql_text()

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_wait_stats

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_wait_stats  Cumulative since last restart or reset

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_wait_stats  Cumulative since last restart or reset  DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_wait_stats  Cumulative since last restart or reset  DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);  Total waits on server

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_wait_stats  Cumulative since last restart or reset  DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);  Total waits on server  Take a delta to see how they are changing

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_wait_stats  Cumulative since last restart or reset  DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);  Total waits on server  Take a delta to see how they are changing  signal_wait_time_ms  Time from when the waiting task has its resource until it starts running  Waiting on CPU thread

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_waiting_tasks

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_waiting_tasks  Tasks currently waiting on a resource

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_waiting_tasks  Tasks currently waiting on a resource  wait_duration_ms

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_waiting_tasks  Tasks currently waiting on a resource  wait_duration_ms  wait_type

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_waiting_tasks  Tasks currently waiting on a resource  wait_duration_ms  wait_type  blocking_session_id

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_os_waiting_tasks  Tasks currently waiting on a resource  wait_duration_ms  wait_type  blocking_session_id  resource_description

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_exec_requests

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_exec_requests  Currently active requests  Shows wait stats too!  session_id  request_id – for parallel tasks  start_time  status – suspended = waiting  command  database_id  blocking_session_id  wait_type  wait_time  last_wait_type – if not currently waiting  wait_resource

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_exec_sessions

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_exec_sessions  Currently active sessions  Shows client connection info  Not all sessions have a request  Has some performance stats cumulative over all requests for the entire session  program_name  is_user_process

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_exec_query_plan()  Query plan from cache  Requires plan_handle

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries  sys.dm_exec_query_plan()  Query plan from cache  Requires plan_handle  sys.dm_exec_sql_text()  SQL text from cache  Requires sql_handle or plan_handle  Provides offset values to identify the currently executing statement in a batch

Diagnosing Performance with Wait Statistics  SOS_SCHEDULER_YIELD

Diagnosing Performance with Wait Statistics  SOS_SCHEDULER_YIELD  SOS: SQLOS

Diagnosing Performance with Wait Statistics  SOS_SCHEDULER_YIELD  SOS: SQLOS  SCHEDULER: manages worker threads onto CPU threads

Diagnosing Performance with Wait Statistics  SOS_SCHEDULER_YIELD  SOS: SQLOS  SCHEDULER: manages worker threads onto CPU threads  YIELD: Giving way to another

Diagnosing Performance with Wait Statistics  SOS_SCHEDULER_YIELD  SOS: SQLOS  SCHEDULER: manages worker threads onto CPU threads  YIELD: Giving way to another  Waiting for another worker thread to yield the CPU thread

Diagnosing Performance with Wait Statistics  PAGE_LATCH / PAGE_IO_LATCH

Diagnosing Performance with Wait Statistics  PAGE_LATCH / PAGE_IO_LATCH  PAGE: unit of data storage in SQL Server

Diagnosing Performance with Wait Statistics  PAGE_LATCH / PAGE_IO_LATCH  PAGE: unit of data storage in SQL Server  IO: reading (I) and writing (O), in this case disk IO

Diagnosing Performance with Wait Statistics  PAGE_LATCH / PAGE_IO_LATCH  PAGE: unit of data storage in SQL Server  IO: reading (I) and writing (O), in this case disk IO  LATCH: Lightweight locking mechanism

Diagnosing Performance with Wait Statistics  PAGE_LATCH / PAGE_IO_LATCH  PAGE: unit of data storage in SQL Server  IO: reading (I) and writing (O), in this case disk IO  LATCH: Lightweight locking mechanism  Waiting for a latch on a page in memory or a page on disk

Diagnosing Performance with Wait Statistics  CXPACKET

Diagnosing Performance with Wait Statistics  CXPACKET  CX: Communication eXchange

Diagnosing Performance with Wait Statistics  CXPACKET  CX: Communication eXchange  PACKET: unit of communication

Diagnosing Performance with Wait Statistics  CXPACKET  CX: Communication eXchange  PACKET: unit of communication  Parallelism is occurring

Diagnosing Performance with Wait Statistics  NETWORK_IO

Diagnosing Performance with Wait Statistics  NETWORK_IO  NETWORK: External communication

Diagnosing Performance with Wait Statistics  NETWORK_IO  NETWORK: External communication  IO: Reading (I) and writing (O)

Diagnosing Performance with Wait Statistics  NETWORK_IO  NETWORK: External communication  IO: Reading (I) and writing (O)  SQL is writing faster than the client is reading

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_xxxxx

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_xxxxx  PREEMPTIVE: Non-yielding

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_xxxxx  PREEMPTIVE: Non-yielding  OS: Operating System

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_xxxxx  PREEMPTIVE: Non-yielding  OS: Operating System  xxxxx: The OS operation or API being called  Non-yielding shell out to the Operating System

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_AUTHENTICATIONOPS

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_AUTHENTICATIONOPS  PREEMPTIVE: Non-yielding  OS: Operating System

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_AUTHENTICATIONOPS  PREEMPTIVE: Non-yielding  OS: Operating System  AUTHENTICATIONOPS: The OS operation or API being called

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_AUTHENTICATIONOPS  PREEMPTIVE: Non-yielding  OS: Operating System  AUTHENTICATIONOPS: The OS operation or API being called, a group of API calls related to authentication

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_AUTHENTICATIONOPS  PREEMPTIVE: Non-yielding  OS: Operating System  AUTHENTICATIONOPS: The OS operation or API being called, a group of API calls related to authentication  Non-yielding shell out to the OS to perform authentication operations

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_VERIFYSIGNATURE

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_VERIFYSIGNATURE  PREEMPTIVE: Non-yielding  OS: Operating System  VERIFYSIGNATURE: The OS operation or API being called

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_VERIFYSIGNATURE  PREEMPTIVE: Non-yielding  OS: Operating System  VERIFYSIGNATURE: The OS operation or API being called  Let’s Look it Up

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_VERIFYSIGNATURE  PREEMPTIVE: Non-yielding  OS: Operating System  VERIFYSIGNATURE: The OS operation or API being called  Verifies if a digital signature matches the signature used to encrypt data

Diagnosing Performance with Wait Statistics  PREEMPTIVE_OS_VERIFYSIGNATURE  PREEMPTIVE: Non-yielding  OS: Operating System  VERIFYSIGNATURE: The OS operation or API being called  Let’s Look it Up

Diagnosing Performance with Wait Statistics  Troubleshooting Slow Queries

Diagnosing Performance with Wait Statistics  Resources  optimization optimization   

Diagnosing Performance with Wait Statistics

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