DB Space Percentage Change

Microsoft.SQLServer.2012.Database.DBSizePercentageChangeMonitor (UnitMonitor)

Monitors for a large change in value of database free space over a set number of sample periods.

Knowledge Base article:

Summary

Monitors for a large change in value of database free space over a set number of sample periods. A rapid large change in value could indicate a problem.

Causes

Unhealthy state is caused by a large change in free space over a set number of sample periods. This can be caused by:

A large autogrowthth setting for a file set to autogrowth.
A fast growing file that consumed a large amount of free space within a short period.
A foreign object or file consumed a large amount of free space hosted on the same disk as this file

Use the following link to view the performance data: Database Performance Data

This monitor aggregates the space available for each file within a Filegroup depending on each file configuration:

No Autogrowth

For a file that has no autogrowth, free space would be the difference between the initial size for a file and the used space.

Autogrowth Enabled

In addition to the difference between the file size and the used space, the free space for files with autogrowth enabled would be the minimum of either the difference between the max size and the file size and the free space left on disk.

The free space calculations also take into account that the file can also fail to grow if the growth amount of the file is greater than the amount left on disk, and that the file cannot grow if the difference between the max size and the current file size is less than the growth amount. In these situations, available free space left on disk is not included as a part of the free space, because we cannot grow any longer.

Resolutions

This issue may be resolved by either:

Decreasing the growth amount for files with autogrowth
Modifying the thresholds for this monitor to suit the workload
Alternatively, if space percentage change is not a concern for the database:
- Disable this monitor for this specific database or all databases

Overrideable Parameters

Name	Description	Default Value
Alert Priority	Defines Alert Priority.	Normal
Alert Severity	Defines Alert Severity.	MatchMonitorHealth
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.	900
Lower Threshold	The lower threshold for this monitor.	25
Number of Samples	Indicates how many times a measured value should breach a threshold before the state is changed.	5
Synchronization Time	The synchronization time specified by using a 24-hour format. May be omitted.
Timeout (seconds)	Specifies the time the workflow is allowed to run before being closed and marked as failed.	300
Upper Threshold	The upper threshold for this monitor.	45

Element properties:

Target

Microsoft.SQLServer.2012.Database

Parent Monitor

Microsoft.SQLServer.2012.Database.DBSpaceMonitor

Category

PerformanceHealth

Enabled

False

Alert Generate

True

Alert Severity

MatchMonitorHealth

Alert Priority

Normal

Alert Auto Resolve

True

Monitor Type

Microsoft.SQLServer.2012.DBPercentageChange

Remotable

True

Accessibility

Public

Alert Message

Significant Percentage Change in DB Total Free Space

The database {2} in SQL instance {1} on computer {0} has experienced a significant change in free space. See “alert context” tab for more details.

RunAs

Default

Source Code:

<UnitMonitor ID="Microsoft.SQLServer.2012.Database.DBSizePercentageChangeMonitor" Accessibility="Public" Enabled="false" Target="SQL2012Core!Microsoft.SQLServer.2012.Database" ParentMonitorID="Microsoft.SQLServer.2012.Database.DBSpaceMonitor" Remotable="true" Priority="Normal" TypeID="Microsoft.SQLServer.2012.DBPercentageChange" ConfirmDelivery="false">

  <Category>PerformanceHealth</Category>

  <AlertSettings AlertMessage="Microsoft.SQLServer.2012.Database.DBSizePercentageChangeMonitor.AlertMessage">

    <AlertOnState>Warning</AlertOnState>

    <AutoResolve>true</AutoResolve>

    <AlertPriority>Normal</AlertPriority>

    <AlertSeverity>MatchMonitorHealth</AlertSeverity>

    <AlertParameters>

      <AlertParameter1>$Target/Host/Host/Property[Type="Windows!Microsoft.Windows.Computer"]/NetworkName$</AlertParameter1>

      <AlertParameter2>$Target/Host/Property[Type="SQL!Microsoft.SQLServer.ServerRole"]/InstanceName$</AlertParameter2>

      <AlertParameter3>$Target/Property[Type="SQL!Microsoft.SQLServer.Database"]/DatabaseName$</AlertParameter3>

    </AlertParameters>

  </AlertSettings>

  <OperationalStates>

    <OperationalState ID="UnderThreshold1" MonitorTypeStateID="UnderThreshold1" HealthState="Success"/>

    <OperationalState ID="OverThreshold1UnderThreshold2" MonitorTypeStateID="OverThreshold1UnderThreshold2" HealthState="Warning"/>

    <OperationalState ID="OverThreshold2" MonitorTypeStateID="OverThreshold2" HealthState="Error"/>

  </OperationalStates>

  <Configuration>

    <IntervalSeconds>900</IntervalSeconds>

    <SyncTime/>

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

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

    <SqlInstanceName>$Target/Host/Property[Type="SQL!Microsoft.SQLServer.ServerRole"]/InstanceName$</SqlInstanceName>

    <ObjectName>$Target/Host/Property[Type="SQL!Microsoft.SQLServer.DBEngine"]/PerformanceCounterObject$:Database</ObjectName>

    <CounterName>DB Total Free Space (%)</CounterName>

    <InstanceName/>

    <DatabaseName>$Target/Property[Type="SQL!Microsoft.SQLServer.Database"]/DatabaseName$</DatabaseName>

    <Value>$Data/Property[@Name='DBFreeSpacePercent']$</Value>

    <Threshold1>25</Threshold1>

    <Threshold2>45</Threshold2>

    <NumSamples>5</NumSamples>

    <TimeoutSeconds>300</TimeoutSeconds>

  </Configuration>

</UnitMonitor>