04 July 2012

Buffer pressure

by Grant Fritchey

Metrics install automatically if you have Redgate Monitor installed.

If you are using Redgate’s SQL Server monitoring tool, Redgate Monitor, you can instantly install and run this metric on your servers.

Trying to determine if you have pressure in your buffer allocations can be difficult. Buffer cache hit ratio is an almost useless metric, so you need a mechanism to let you know if there’s a problem in that area. You can use SQL Server Memory Manager Object and then compare the Target Server Memory to the Total Server Memory allocations. Target Server Memory is essentially the ideal amount of memory the server can consume, while Total Server Memory specifies the amount of memory the server has committed using the memory manager. When the target is below the current committed, you’re looking at a buffer issue. This query simply compares the two with subtraction so that you’ll know when you’re looking at negative numbers you’ve hit a buffer problem.

Metric definition

Name

Buffer pressure

Description

Uses the difference between "Target Server Memory" and "Total Server Memory" from SQL Server Memory Manager Object.

The T-SQL query that will collect data


		
			
			
Transact-SQL
			
			SELECT  (     
    SELECT    cntr_value   
    FROM      sys.dm_os_performance_counters    
    WHERE     counter_name = 'Target Server Memory (KB)'
) - (     
    SELECT    cntr_value    
    FROM      sys.dm_os_performance_counters   
    WHERE     counter_name = 'Total Server Memory (KB)'
) [Buffer Pressure];
			
				
					
				
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						SELECT  (     
    SELECT    cntr_value   
    FROM      sys.dm_os_performance_counters    
    WHERE     counter_name = 'Target Server Memory (KB)'
) - (     
    SELECT    cntr_value    
    FROM      sys.dm_os_performance_counters   
    WHERE     counter_name = 'Total Server Memory (KB)'
) [Buffer Pressure];

Instances to collect from

Select all

Databases to collect from

master

Collection frequency

Use collected or calculated values

Leave the Use a calculated rate of change between collections check box unchecked

Metric collection

Enabled

Alert definition

Alert name

Buffer pressure detected

Description

Any time the target value is greater than the allocated value, you have a buffer memory allocation issue.

Raise an alert when the metric value goes

Below the defined threshholds

Default threshold values

High:	0
Medium:	Turn off check box
Low:	Turn off check box

Raise an alert when the threshold is passed for

1 collection

Alert is

Enabled

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Buffer pressure

Metric definition

Name

Description

The T-SQL query that will collect data

Instances to collect from

Databases to collect from

Collection frequency

Use collected or calculated values

Metric collection

Alert definition

Alert name

Description

Raise an alert when the metric value goes

Default threshold values

Raise an alert when the threshold is passed for

Alert is

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