Updating views in sql server Erstes kennenlernen schule

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As the query continues updating more records in the table, it won’t acquire any more locks, but any data and index pages that are updated in memory must be EX (exclusive) latched before the update can occur.The latch acts as the synchronization mechanism to prevent two threads updating the page at the same time, or a thread reading the page while another is in the middle of updating it.This started out as a small post but grew into a 10-page, 2500 word article :-) Here are the results (in each of the Other values, a few people asked what DMVs are – see Dynamic Management Views and Functions in BOL).Other values: The survey results are not surprising, especially among readers of my blog.In a medium to enterprise-scale distributed deployment, the SQL Server instance should be located on a dedicated standalone server or in a SQL Server high-availability configuration.In either case, SQL Server must already exist and is accessible before you start the installation of the first management server or ACS collector.Typically you or they are going to make use of four DMVs that give increasingly advanced information about what’s going on for use in performance troubleshooting: A few weeks ago I kicked off a survey to find out whether you’ve heard of or used these DMVs.

One example of locks and latches – imagine a table where an update query has caused lock escalation so that a table X lock is held on the table.The code captures the output from the DMV into two temp tables, with whatever time period you want in between (to allow you to run a command), and then shows the difference between the two sets of data.I’ll show an example of running IF EXISTS (SELECT * FROM [tempdb].[sys].[objects] WHERE [name] = N'##Temp Spinlock Stats1') DROP TABLE [##Temp Spinlock Stats1]; IF EXISTS (SELECT * FROM [tempdb].[sys].[objects] WHERE [name] = N'##Temp Spinlock Stats2') DROP TABLE [##Temp Spinlock Stats2]; GO -- Baseline SELECT * INTO [##Temp Spinlock Stats1] FROM sys.dm_os_spinlock_stats WHERE [collisions] 0 ORDER BY [name]; GO -- Now do something DBCC CHECKDB (N'Sales DB') WITH NO_INFOMSGS; GO -- Capture updated stats SELECT * INTO [##Temp Spinlock Stats2] FROM sys.dm_os_spinlock_stats WHERE [collisions] 0 ORDER BY [name]; GO -- Diff them SELECT '***' AS [New], [ts2].[name] AS [Spinlock], [ts2].[collisions] AS [Diff Collisions], [ts2].[spins] AS [Diff Spins], [ts2].[spins_per_collision] AS [Spins Per Collision], [ts2].[sleep_time] AS [Diff Sleep Time], [ts2].[backoffs] AS [Diff Backoffs] FROM [##Temp Spinlock Stats2] [ts2] LEFT OUTER JOIN [##Temp Spinlock Stats1] [ts1] ON [ts2].[name] = [ts1].[name] WHERE [ts1].[name] IS NULL UNION SELECT '' AS [New], [ts2].[name] AS [Spinlock], [ts2].[collisions] - [ts1].[collisions] AS [Diff Collisions], [ts2].[spins] - [ts1].[spins] AS [Diff Spins], CASE ([ts2].[spins] - [ts1].[spins]) WHEN 0 THEN 0 ELSE ([ts2].[spins] - [ts1].[spins]) / ([ts2].[collisions] - [ts1].[collisions]) END AS [Spins Per Collision], [ts2].[sleep_time] - [ts1].[sleep_time] AS [Diff Sleep Time], [ts2].[backoffs] - [ts1].[backoffs] AS [Diff Backoffs] FROM [##Temp Spinlock Stats2] [ts2] LEFT OUTER JOIN [##Temp Spinlock Stats1] [ts1] ON [ts2].[name] = [ts1].[name] WHERE [ts1].[name] IS NOT NULL AND [ts2].[collisions] - [ts1].[collisions] New Spinlock Diff Collisions Diff Spins Spins Per Collision Diff Sleep Time Diff Backoffs ---- ------------------ -------------------- -------------------- ----------------- -------------------- ------------ *** DBCC_CHECK 4 24 6 0 0 *** DIAG_MANAGER 1 0 0 0 0 *** FCB_REPLICA_SYNC 10 16147 1614.7 0 0 *** LSID 9 0 0 0 0 *** QUERYEXEC 5 0 0 0 0 *** X_PACKET_LIST 2 0 0 0 0 *** X_PORT 8 227 28.375 0 0 *** XACT_WORKSPACE 11 0 0 0 0 *** XID_ARRAY 7 0 0 0 0 BUF_FREE_LIST 2 0 0 0 0 HOBT_HASH 2 1 0 0 0 LOCK_HASH 3 1818 606 0 0 SOS_RW 2 500 250 0 0 SOS_SCHEDULER 5 6 1 0 0 SOS_SUSPEND_QUEUE 11 39 3 0 0 SOS_TASK 1 0 0 0 0 SOS_TLIST 1 0 0 0 0 commands – those marked with *** did not appear in the ‘before’ set of spinlock stats. You can also investigate spinlocks using extended events – again, more on that in future.By analyzing which resources (and combinations of resource) are being waited for the most, you can get an idea of where to start digging in further.An example might be that if most of the waits are DMV, giving links to resources, and explaining the most common ones that people see in the field based on data from more than 1800 SQL Servers – see Wait statistics, or please tell me where it hurts.

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