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MySQL Server Table Cache Hit Percent Monitor

Microsoft.MySQLServer.ManagedServer.Unix.TableCacheHitPct.Monitor (UnitMonitor)

Knowledge Base article:

Summary

The percentage of number of waits to gain a lock on the MyISAM table versus the number of locks requested. MySQL uses table-level locking for MyISAM, MEMORY, and MERGE tables. The monitor threshold is analyzed against an average of values returned in polls to the agent where the Number of Samples parameter controls the number of samples included in the calculation of the average.

Causes

An unhealthy state indicates the percentage of table cache hit rate is low. The table cache might not have enough storage to hold tables open. Additionally, an excessive amount of concurrent connections can cause rapid decrease in table cache storage.

Resolutions

To address low table hit percent increase the table_cache size to allow additional tables to be stored.

Configuration

Default Configuration

Parameter

Default Value

Warning Threshold

Less than 80

Error Threshold

Less than 70

Number of Samples

3

Overrides can be used to change the parameter values defined above for all instances or for specific instances or groups.

Element properties:

TargetMicrosoft.MySQLServer.ManagedServer.Unix
Parent MonitorMicrosoft.MySQLServer.TableCachePerformanceRollup
CategoryPerformanceHealth
EnabledTrue
Alert GenerateTrue
Alert SeverityMatchMonitorHealth
Alert PriorityNormal
Alert Auto ResolveTrue
Monitor TypeMicrosoft.Oss.WSManEnumeration.LessThanThreshold.ThreeState.MonitorType
RemotableTrue
AccessibilityPublic
Alert Message
MySQL Server Table Cache Hit Percent
The current Table Cache Hit Percent ({0}\%) for the MySQL Server is low
RunAsDefault

Source Code:

<UnitMonitor ID="Microsoft.MySQLServer.ManagedServer.Unix.TableCacheHitPct.Monitor" Accessibility="Public" Target="Microsoft.MySQLServer.ManagedServer.Unix" TypeID="Oss!Microsoft.Oss.WSManEnumeration.LessThanThreshold.ThreeState.MonitorType" Enabled="onStandardMonitoring" ParentMonitorID="Microsoft.MySQLServer.TableCachePerformanceRollup">

  <Category>PerformanceHealth</Category>

  <AlertSettings AlertMessage="Microsoft.MySQLServer.ManagedServer.Unix.TableCacheHitPct.AlertMessage">

    <AlertOnState>Warning</AlertOnState>

    <AutoResolve>true</AutoResolve>

    <AlertPriority>Normal</AlertPriority>

    <AlertSeverity>MatchMonitorHealth</AlertSeverity>

    <AlertParameters>

      <AlertParameter1>$Data/Context/Value$</AlertParameter1>

    </AlertParameters>

  </AlertSettings>

  <OperationalStates>

    <OperationalState HealthState="Success" MonitorTypeStateID="StatusOK" ID="OverThreshold"/>

    <OperationalState HealthState="Warning" MonitorTypeStateID="StatusWarning" ID="UnderWarningThreshold"/>

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

  </OperationalStates>

  <Configuration>

    <Interval>300</Interval>

    <TargetSystem>$Target/Host/Property[Type="Unix!Microsoft.Unix.Computer"]/NetworkName$</TargetSystem>

    <Uri>http://schemas.microsoft.com/wbem/wscim/1/cim-schema/2/MySQL_ServerStatistics?__cimnamespace=root/mysql</Uri>

    <WSManFilter/>

    <ObjectName>MySQL Server</ObjectName>

    <CounterName>Table Cache Hit Pct</CounterName>

    <InstanceXPath>/DataItem/WsManData/*[local-name(.)='MySQL_ServerStatistics']/*[local-name(.)='InstanceID']</InstanceXPath>

    <InstanceName>$Target/Property[Type="Microsoft.MySQLServer.Installation"]/InstanceID$</InstanceName>

    <Value>$Data/WsManData/*[local-name(.)='MySQL_ServerStatistics']/*[local-name(.)='TCacheHitPct']$</Value>

    <WarningThreshold>80</WarningThreshold>

    <ErrorThreshold>70</ErrorThreshold>

    <NumSamples>3</NumSamples>

  </Configuration>

</UnitMonitor>