Buffer Cache Hit Ratio

Microsoft.SQLServer.Linux.Monitor.DBEngine.BufferCacheHitRatio (UnitMonitor)

Buffer Cache Hit Ratio for DB Engine. The monitor is disabled by default. Use overrides to enable it when necessary.

Knowledge Base article:

Summary

Buffer Cache Hit Ratio monitor for SQL DB Engine

Percentage of pages that were found in the buffer pool without having to incur a read from disk.

Causes

Zero value indicates memory bottleneck - SQL Server cannot efficiently cache the data pages in memory; reads from disk are relatively high.

Resolutions

Increase available memory on the server.
Increase 'Max memory'.
Provide index optimization.

Overridable Parameters

Name	Description	Default Value
Alert Priority	Defines Alert Priority.	Normal
Alert Severity	Defines Alert Severity.	Error
Enabled	Enables or disables the workflow.	No
Generates Alerts	Defines whether the workflow generates an Alert.	Yes
Interval (seconds)	The recurring interval of time in seconds in which to run the workflow.	300
Number of samples	Indicates how many times a measured value should breach a threshold before the state is changed.	6
Synchronization Time	The synchronization time specified by using a 24-hour format. May be omitted.
Threshold	The collected value will be compared against this parameter.	90
Timeout (seconds)	Specifies the time the workflow is allowed to run before being closed and marked as failed.	200
Timeout for query execution (seconds)	The workflow will fail and register an event, if the query execution takes longer than the specified period.	60
Timeout for database connection (seconds)	The workflow will fail and register an event, if it cannot access the database during the specified period.	15

Element properties:

Target

Microsoft.SQLServer.Linux.DBEngine

Parent Monitor

System.Health.PerformanceState

Category

PerformanceHealth

Enabled

False

Alert Generate

True

Alert Severity

Error

Alert Priority

Normal

Alert Auto Resolve

True

Monitor Type

Microsoft.SQLServer.Linux.MonitorType.DBEngine.BufferCacheHitRatio

Remotable

True

Accessibility

Public

Alert Message

MSSQL on Linux: Cache Hit Ratio is too low

The buffer cache hit ratio on SQL Server instance "{1}", computer "{0}" is too low. See the "Alert Context" tab for more details.

RunAs

Default

Source Code:

<UnitMonitor ID="Microsoft.SQLServer.Linux.Monitor.DBEngine.BufferCacheHitRatio" Accessibility="Public" Enabled="false" Target="SqlDiscL!Microsoft.SQLServer.Linux.DBEngine" ParentMonitorID="Health!System.Health.PerformanceState" Remotable="true" Priority="Normal" TypeID="Microsoft.SQLServer.Linux.MonitorType.DBEngine.BufferCacheHitRatio" ConfirmDelivery="false">

  <Category>PerformanceHealth</Category>

  <AlertSettings AlertMessage="Microsoft.SQLServer.Linux.Monitor.DBEngine.BufferCacheHitRatio.AlertMessage">

    <AlertOnState>Error</AlertOnState>

    <AutoResolve>true</AutoResolve>

    <AlertPriority>Normal</AlertPriority>

    <AlertSeverity>Error</AlertSeverity>

    <AlertParameters>

      <AlertParameter1>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/MachineName$</AlertParameter1>

      <AlertParameter2>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/InstanceName$</AlertParameter2>

    </AlertParameters>

  </AlertSettings>

  <OperationalStates>

    <OperationalState ID="Normal" MonitorTypeStateID="Normal" HealthState="Success"/>

    <OperationalState ID="Error" MonitorTypeStateID="Error" HealthState="Error"/>

  </OperationalStates>

  <Configuration>

    <MachineName>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/MachineName$</MachineName>

    <NetbiosComputerName>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/NetbiosComputerName$</NetbiosComputerName>

    <InstanceName>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/InstanceName$</InstanceName>

    <ConnectionString>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/ConnectionString$</ConnectionString>

    <InstanceVersion>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/Version$</InstanceVersion>

    <InstanceEdition>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/Edition$</InstanceEdition>

    <IntervalSeconds>300</IntervalSeconds>

    <SyncTime/>

    <Threshold>90</Threshold>

    <NumSamples>6</NumSamples>

    <TimeoutSeconds>200</TimeoutSeconds>

    <SqlExecTimeoutSeconds>60</SqlExecTimeoutSeconds>

    <SqlTimeoutSeconds>15</SqlTimeoutSeconds>

    <PerformanceCounterObject>$Target/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/PerformanceCounterObject$</PerformanceCounterObject>

  </Configuration>

</UnitMonitor>