{"id":488,"date":"2012-05-10T02:26:00","date_gmt":"2012-05-10T02:26:00","guid":{"rendered":"\/blogs\/paul\/post\/Survey-most-prevalent-latch-waits.aspx"},"modified":"2016-05-23T17:02:32","modified_gmt":"2016-05-24T00:02:32","slug":"survey-most-prevalent-latch-waits-code-to-run","status":"publish","type":"post","link":"https:\/\/www.sqlskills.com\/blogs\/paul\/survey-most-prevalent-latch-waits-code-to-run\/","title":{"rendered":"Survey: most prevalent latch waits (code to run)"},"content":{"rendered":"

I first started blogging about latches and some of the deeper parts of SQL Server internals last year (see <\/span>Advanced performance troubleshooting: waits, latches, spinlocks<\/span><\/a>) and now I’d like to pick up that thread (no scheduling pun intended :-)) and blog some more about some of the common latches that could be a performance bottleneck.<\/span><\/p>\n

To that end, I’ve got some code below (plus example output)\u00a0that will show the most common latch waits that have occurred on your system.<\/span><\/p>\n

WITH Latches AS
\n(SELECT
\nlatch_class,
\nwait_time_ms \/ 1000.0 AS WaitS,
\nwaiting_requests_count AS WaitCount,
\n100.0 * wait_time_ms \/ SUM (wait_time_ms) OVER() AS Percentage,
\nROW_NUMBER() OVER(ORDER BY wait_time_ms DESC) AS RowNum
\nFROM sys.dm_os_latch_stats
\nWHERE latch_class NOT IN (
\n‘BUFFER’)
\nAND wait_time_ms > 0<\/span>
\n)
\nSELECT
\nW1.latch_class AS LatchClass,
\nCAST (W1.WaitS AS DECIMAL(14, 2)) AS Wait_S,
\nW1.WaitCount AS WaitCount,
\nCAST (W1.Percentage AS DECIMAL(14, 2)) AS Percentage,
\nCAST ((W1.WaitS \/ W1.WaitCount) AS DECIMAL (14, 4)) AS AvgWait_S
\nFROM Latches AS W1
\nINNER JOIN Latches AS W2
\nON W2.RowNum <= W1.RowNum
\nWHERE W1.WaitCount > 0
\nGROUP BY W1.RowNum, W1.latch_class, W1.WaitS, W1.WaitCount, W1.Percentage
\nHAVING SUM (W2.Percentage) – W1.Percentage < 95; — percentage threshold
\nGO<\/span><\/p>\n

LatchClass\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Wait_S\u00a0 WaitCount\u00a0 Percentage\u00a0 AvgWait_S
\n——————————— ——- ———- ———– ———-
\nLOG_MANAGER\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 221.43\u00a0 4659\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 45.81\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0.0475
\nACCESS_METHODS_HOBT_VIRTUAL_ROOT\u00a0 199.56\u00a0 7017\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 41.28\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0.0284
\nFGCB_ADD_REMOVE\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 35.17\u00a0\u00a0 1047\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 7.27\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0.0336
\nDBCC_OBJECT_METADATA\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 26.85\u00a0\u00a0 256490\u00a0\u00a0\u00a0\u00a0 5.55\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0.0001
\n<\/span><\/p><\/blockquote>\n

I’d like you to run the code and send me the output (either as a comment or in email<\/a>). I’ll collate all your output and do some blogging for your enjoyment. [Update: I don’t need any more data – thanks!]<\/span><\/p>\n

Thanks!<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

I first started blogging about latches and some of the deeper parts of SQL Server internals last year (see Advanced performance troubleshooting: waits, latches, spinlocks) and now I’d like to pick up that thread (no scheduling pun intended :-)) and blog some more about some of the common latches that could be a performance bottleneck. […]<\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[55,66,91,101],"tags":[],"class_list":["post-488","post","type-post","status-publish","format-standard","hentry","category-latches","category-performance-tuning","category-surveys","category-wait-stats"],"yoast_head":"\nSurvey: most prevalent latch waits (code to run) - Paul S. Randal<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.sqlskills.com\/blogs\/paul\/survey-most-prevalent-latch-waits-code-to-run\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Survey: most prevalent latch waits (code to run) - Paul S. Randal\" \/>\n<meta property=\"og:description\" content=\"I first started blogging about latches and some of the deeper parts of SQL Server internals last year (see Advanced performance troubleshooting: waits, latches, spinlocks) and now I’d like to pick up that thread (no scheduling pun intended :-)) and blog some more about some of the common latches that could be a performance bottleneck. 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