Performance Tuning with SQL Server Dynamic Management Views

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Chapter 7: OS and Hardware Interaction Returned will be values such as the following: object_name instance_name counter_name cntr_value -------------------------------- -------------- ------------------------------ -------------- -- SQLServer:Latches Average Latch Wait Time (ms) 3.84907340420574 SQLServer:Locks _Total Average Wait Time (ms) 188.428878069211 SQLServer:Locks AllocUnit Average Wait Time (ms) NULL SQLServer:Locks Application Average Wait Time (ms) 263.055555555556 SQLServer:Locks Database Average Wait Time (ms) NULL SQLServer:Locks Extent Average Wait Time (ms) NULL SQLServer:Locks File Average Wait Time (ms) 471.392592592593 SQLServer:Locks HoBT Average Wait Time (ms) NULL SQLServer:Locks Key Average Wait Time (ms) 150.459888113501 SQLServer:Locks Metadata Average Wait Time (ms) 95.7042253521127 SQLServer:Locks Object Average Wait Time (ms) 610.405089408528 SQLServer:Locks Page Average Wait Time (ms) 399.793103448276 SQLServer:Locks RID Average Wait Time (ms) 1860 From this output, we can see that we've no waiting on Database, Extent, and HoBT (heap or B-tree) objects, but have spent an average of 263 milliseconds on Application locks (which are used on this particular system to implement single-threaded reads from a queue), 150 milliseconds on Key locks, and 399 on Page locks, amongst others. Monitoring Machine Characteristics A common task for DBAs is to monitor the configurations and characteristics of their servers, as well as to track changes to these settings over time. The sys.dm_os_sys_ info DMV contains a host of values that will give you a basic understanding of how the interface between the OS and SQL Server is configured. It returns a single row, summarizing the characteristics of a given machine, in terms of static configuration, such as the number of processors, as well as how long a server has been running. Columns represented in the view include those listed below. 288
• cpu_count – number of logical processors on the computer. 289 Chapter 7: OS and Hardware Interaction • hyperthread_ratio – ratio of logical to physical processors (cores). For example, on a dual-core processor with hyper-threading turned off, this value would be 2. If hyper-threading were enabled, the value would be 4. Note that this ratio value does not discern between hyper-threading and multi-core (e.g. a quad-core processor with no hyper-threading would also return a value of 4). • physical_memory_in_bytes – total amount of physical RAM installed on the computer or, at least, the amount of RAM that the OS believes it has available (a distinction that is particularly relevant when dealing with virtual environments). • virtual_memory_in_bytes – amount of virtual RAM available to the process in user mode. This can differ depending on the OS. On a 32-bit OS, variations can be based on the 3-GB switch or, in Vista and later, the IncreaseUserVa switch (set using the bcdedit utility). • max_workers_count – maximum number of workers that can be created. Workers do the work for SQL Server and are generally equivalent to threads, unless running in "lightweight pooling" server configuration, in which case it corresponds to a fiber (for a deeper understanding, go to http://msdn.microsoft.com/en-us/library/ ms189267.aspx). • scheduler_total_count – total number of schedulers configured, including the system schedulers, such as the one that handles Dedicated Administrator Connection (DAC) connections (corresponds to the result of: select count(*) from sys. dm_os_schedulers). • scheduler_count – current number of schedulers that are visible to user processes (corresponds to the result of select count(*) from sys.dm_os_schedulers where status = 'VISIBLE ONLINE'). • os_priority_class – Windows scheduling priority for the SQL Server process. Essentially, a high value will allow SQL Server to use a higher than normal allocation of OS resources. Domain: 64 (low), 16384 (below normal), 32 (normal), 32768 (above normal), 256 (real-time), 128 (high). The default is "normal," unless the priority boost
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High Performance SQL Server Perform
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Copyright Louis Davidson and Tim Fo
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Dissecting user activity ..........
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Getting Stats about tempdb Usage ..
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Server (PASS) since 2002. He has al
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Tim Ford I dedicate this book to Am
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13 Introduction on those objects th
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Code Examples 15 Introduction Throu
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Chapter 1: Using Dynamic Management
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DMO Security and Permissions Chapte
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We can find out, for example: Chapt
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Beware of the watcher effect Chapte
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Chapter 2: Connections, Sessions an
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Sysprocesses versus DMOs Chapter 2:
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Listing 2.3: Who is connected? Chap
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Listing 2.4: Who is executing what
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Logins with more than one session C
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DECLARE @days_old SMALLINT SELECT @
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• dbcc shrinkdatabase / shrinkfil
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This will return (with a different
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Who is running what, right now? Cha
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Summary Chapter 2: Connections, Ses
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73 Chapter 3: Query Plan Metadata P
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75 Chapter 3: Query Plan Metadata P
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77 Chapter 3: Query Plan Metadata t
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SELECT TOP 10 object_id , name FROM
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Dissecting the SQL text 83 Chapter
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Figure 3.2: Three queries returned
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87 Chapter 3: Query Plan Metadata T
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89 Chapter 3: Query Plan Metadata
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Criteria in determing plan reuse 91
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For a server that had been up for t
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Listing 3.9: Investigating the most
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SELECT FirstName , LastName FROM db
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99 Chapter 3: Query Plan Metadata C
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Listing 3.14: Finding the CPU-inten
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WHERE execText.text like '%account%
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115 Chapter 4: Transactions We'll a
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117 Chapter 4: Transactions unique
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Snapshot isolation level 119 Chapte
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121 Chapter 4: Transactions • res
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Lock types 123 Chapter 4: Transacti
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127 Chapter 4: Transactions SELECT
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129 Chapter 4: Transactions If, fro
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131 Chapter 4: Transactions The LEF
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133 Chapter 4: Transactions When in
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135 Chapter 4: Transactions column.
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137 Chapter 4: Transactions some po
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139 Chapter 4: Transactions OPENTRA
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141 Chapter 4: Transactions In this
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143 Chapter 4: Transactions time on
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145 Chapter 4: Transactions process
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INNER JOIN sys.dm_tran_session_tran
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149 Chapter 4: Transactions Any DML
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SELECT SD.[name] , SD.snapshot_isol
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FROM dbo.Culture ; -- COMMIT; Listi
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161 Chapter 4: Transactions In orde
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163 Chapter 4: Transactions In shor
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Using sys.dm_tran_version_store 165
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167 Chapter 4: Transactions In List
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sys.dm_tran_top_version_generators
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171 Chapter 4: Transactions Via que
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Chapter 5: Indexing Strategy and Ma
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High selectivity Chapter 5: Indexin
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Identify inefficient indexes Chapte
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Listing 5.9: Retrieving locking and
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Missing index groups Chapter 5: Ind
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Listing 5.13: Finding beneficial mi
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ORDER BY ddips.[avg_fragmentation_i
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Summary Chapter 5: Indexing Strateg
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Chapter 6: Physical Disk Statistics
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Tuning the Disk I/O Subsystem Chapt
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The view returns the statistical co
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The sys.dm_db_index_physical_stats
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The NEWSEQUENTIALID() function Chap
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