Performance Tuning with SQL Server Dynamic Management Views

Chapter 7: OS and Hardware Interaction
As an example usage, the query in Listing 7.11 will return the cache hit ratio from the
buffer manager.
DECLARE @object_name SYSNAME
SET @object_name = CASE WHEN @@servicename = 'MSSQLSERVER' THEN 'SQLServer'
ELSE 'MSSQL$' + @@serviceName
END + ':Buffer Manager'
DECLARE
@PERF_LARGE_RAW_FRACTION INT ,
@PERF_LARGE_RAW_BASE INT
SELECT @PERF_LARGE_RAW_FRACTION = 537003264 ,
@PERF_LARGE_RAW_BASE = 1073939712
SELECT dopc_fraction.object_name ,
dopc_fraction.instance_name ,
dopc_fraction.counter_name ,
--when divisor is 0, return I return NULL to indicate
--divide by 0/no values captured
CAST(dopc_fraction.cntr_value AS FLOAT)
/ CAST(CASE dopc_base.cntr_value
WHEN 0 THEN NULL
ELSE dopc_base.cntr_value
END AS FLOAT) AS cntr_value
FROM sys.dm_os_performance_counters AS dopc_base
JOIN sys.dm_os_performance_counters AS dopc_fraction
ON dopc_base.cntr_type = @PERF_LARGE_RAW_BASE
AND dopc_fraction.cntr_type = @PERF_LARGE_RAW_FRACTION
AND dopc_base.object_name = dopc_fraction.object_name
AND dopc_base.instance_name = dopc_fraction.instance_name
AND ( REPLACE(dopc_base.counter_name,
'base', '') = dopc_fraction.counter_name
--Worktables From Cache has "odd" name where
--Ratio was left off
OR REPLACE(dopc_base.counter_name,
'base', '') = ( REPLACE(dopc_fraction.counter_name,
'ratio', '') )
)
WHERE dopc_fraction.object_name = @object_name
AND dopc_fraction.instance_name = ''
AND dopc_fraction.counter_name = 'Buffer cache hit ratio'
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