Transaction Log Free Space (\%)

Microsoft.SQLServer.Windows.Monitor.Database.TransactionLogSpaceFreePercent (UnitMonitor)

Transaction Log Free Space (\%) monitor for SQL DBs on Windows. Note: This monitor is disabled by default. Please use overrides to enable it when necessary.

Knowledge Base article:

Summary

Transaction Log Free Space (%) monitor for SQL DB

Causes

An unhealthy state is caused by having low free space across all log files. Low free space can be caused by:

Inadequate file configuration settings (size, max size, autogrowth, etc.)
Inadequate space left on media
Lack of periodic regular backups
Log not truncating

Use the following link to view the performance data:

Database Performance Data

This monitor aggregates the space available for each log file within a database depending on each file’s 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.

Low free space for database log files that have autogrowth could mean that the file is approaching the limits of the hosting logical drive. For files with autogrowth enabled with a max size, low free space could also mean that the file is approaching the max size specified for a file.

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 part of the free space because we cannot grow any longer.

Resolutions

This issue may be resolved by either:

Increasing the allocated size for log files if autogrowth is disabled
Increasing the max size value for a log file if autogrowth is enabled
Enabling autogrowth for at least one file
Moving log files to another drive with more free space if growth space is limited
Performing regular backups of log files for FULL and BULK-LOGGED recovery modes
Investigate why log is not getting truncated:
- Long open running active transactions
- Long running backup operations
- Replicated transaction open for a long time (Transactional Replication)
- Mirror lagging behind principal server (Database Mirroring)
Modifying the thresholds for this monitor to suit the workload
Alternatively if log file free space is not a concern for the database:
- Disable this monitor for this specific database or all databases

See SQL Server Books Online: Files and Filegroups Architecture

Overrideable Parameters

Name	Description	Default Value
Alert Priority	Defines Alert Priority.	Normal
Alert Severity	Defines Alert Severity.	Error
Azure Maximum File Size (MB)	The maximum size of data file stored in Azure BLOB Storage. The workflow will consider this value as a maximum storage capacity for each file.	1048576
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
Threshold	The collected value will be compared against this parameter.	10
Timeout (seconds)	Specifies the time the workflow is allowed to run before being closed and marked as failed.	200

Element properties:

Target

Microsoft.SQLServer.Windows.Database

Parent Monitor

Microsoft.SQLServer.Windows.Rollup.Database.DBSpace

Category

PerformanceHealth

Enabled

False

Alert Generate

True

Alert Severity

Error

Alert Priority

Normal

Alert Auto Resolve

True

Monitor Type

Microsoft.SQLServer.Windows.MonitorType.Database.TransactionLogSpaceFreePercent

Remotable

True

Accessibility

Public

Alert Message

MSSQL on Windows: Transaction Log Free Space (\%) is too low

Transaction Log Free Space (\%) of the database "{0}" in SQL instance "{1}" on computer "{2}" is too low. See "Alert Context" tab for more details.

RunAs

Default

Source Code:

<UnitMonitor ID="Microsoft.SQLServer.Windows.Monitor.Database.TransactionLogSpaceFreePercent" Accessibility="Public" Enabled="false" Target="SqlDiscW!Microsoft.SQLServer.Windows.Database" ParentMonitorID="Microsoft.SQLServer.Windows.Rollup.Database.DBSpace" Remotable="true" Priority="Normal" TypeID="Microsoft.SQLServer.Windows.MonitorType.Database.TransactionLogSpaceFreePercent" ConfirmDelivery="false">

  <Category>PerformanceHealth</Category>

  <AlertSettings AlertMessage="Microsoft.SQLServer.Windows.Monitor.Database.TransactionLogSpaceFreePercent.AlertMessage">

    <AlertOnState>Error</AlertOnState>

    <AutoResolve>true</AutoResolve>

    <AlertPriority>Normal</AlertPriority>

    <AlertSeverity>Error</AlertSeverity>

    <AlertParameters>

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

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

      <AlertParameter3>$Target/Host/Property[Type="SqlCoreLib!Microsoft.SQLServer.Core.DBEngine"]/MachineName$</AlertParameter3>

    </AlertParameters>

  </AlertSettings>

  <OperationalStates>

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

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

  </OperationalStates>

  <Configuration>

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

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

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

    <AzureMaxFileSizeMB>1048576</AzureMaxFileSizeMB>

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

    <CounterName>Log Free Space (%)</CounterName>

    <PerfInstanceName/>

    <ValuePropertyName>DBLogFreeSpacePercent</ValuePropertyName>

    <Threshold>10</Threshold>

    <NumSamples>6</NumSamples>

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

    <MonitoringType>$Target/Host/Property[Type="SqlDiscW!Microsoft.SQLServer.Windows.DBEngine"]/MonitoringType$</MonitoringType>

    <SqlTimeoutSeconds>15</SqlTimeoutSeconds>

    <TimeoutSeconds>200</TimeoutSeconds>

    <IntervalSeconds>300</IntervalSeconds>

    <SyncTime/>

  </Configuration>

</UnitMonitor>