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Sql waits
This document discusses waits in SQL Server 2008. It explains that waits occur when a SQL Server worker thread is waiting for a resource to become available, such as waiting for memory, disk I/O, or to stop blocking on a lock. The document lists common wait types including memory, disk I/O, blocking, CPU, and network waits. It also discusses dynamic management views introduced in SQL Server 2005 that provide wait statistics and extended events for monitoring waits.
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Sql waits
- 1. ©2011 Hewlett-Packard DevelopmentCompany, L.P. The information contained herein is subject to change without notice SQL Server 2008 WAITS Miroslav Dimitrov
- 2. How SQL Serverworks ?! • SQL Server OS – Schedulers – Workers Lists to which workers can be assigned: worker waiter runnable I/O timer
- 3. WAITS – Whatare they ?! • SQL Server 2000 – DBCC SQLPERF – ”sysprocesses” system view (waittype column) • SQL Server 2005 - DMVs – sys.dm_os_wait_stats – wait statistics – sys.dm_os_waiting_tasks – task-level wait information • SQL Server 2008 – new waits – Solve the problem with fine-grained analysis of wait statistics in SQL Server 2005
- 4. Types of WAITS •Resource waits • Queue waits • External waits A SQL Server worker thread is not considered to be waiting if any of the following is true: • A resource becomes available. • A queue is nonempty. • An external process finishes.
- 5. Waits • Memory Waits –CMEMTHREAD – RESOURCE_SEMAPHORE • Disk I/O Waits – IO_COMPLETION – ASYNC_IO_COMPLETION – WRITELOG – PAGEIOLATCH_* • Blocking waits – LCK_*
- 6. Waits (continued) • CPU –CXPACKET – SOS_SCHEDULER_YIELD • Network Waits – ASYNC_NETWORK_IO – DBMIRROR_SEND • System waits – LAZYWRITER_SLEEP – REQUEST_FOR_DEADLOCK_SEARCH – SQLTRACE_BUFFER_FLUSH – XE_TIMER_EVENT – FT_IFTS_SCHEDULER_IDLE_WAIT – LOGMGR_QUEUE – CHECKPOINT_QUEUE – SLEEP_TASK – BROKER_TO_FLUSH
- 7. Waits (continued) • PreemptiveWait Types • SQL Server extended events
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- 9. References • http://msdn.microsoft.com/en- us/library/ms179984%28v=SQL.90%29.aspx • http://msdn.microsoft.com/en- us/library/ms179984%28v=SQL.100%29.aspx •http://msdn.microsoft.com/en- us/library/ms179984%28v=SQL.105%29.aspx