Average length of the row chains in the hash buckets

Microsoft.SQLServer.Linux.Monitor.DBFilegroupFx.HashIndexAvgChainLength (UnitMonitor)

This monitor checks Hash Index Empty Buckets Count and Average Length of the Row Chains in the SQL Database.

Knowledge Base article:

Summary

This monitor checks the Average length of the row chains in the hash buckets for tables in this database. Since this monitor is a part of an overall standards requirement, an alert would be generated if the setting does not meet the specified standard.

Configuration

The indexes are used for efficient accessing the data in SQL Server tables. Specifying the right indexes can dramatically improve query performance. The monitor raises a warning alert if empty_bucket_percent is greater than Empty Bucket Percent Threshold, and avg_chain_length is greater than Average Chain Length Threshold, there are too many duplicates, and usage of NONCLUSTERED index would be more appropriate.

External

See the detailed information:

Indexes for Memory-Optimized Tables

Overridable Parameters

Name	Description	Default Value
Alert Priority	Defines Alert Priority.	Normal
Alert Severity	Defines Alert Severity.	Warning
Average Chain Length Threshold	Threshold for Average Chain Length that indicates the average length of the row chains in the hash buckets.	100
Display index count	The display count of not configured indexes according to the best practice.	5
Empty Bucket Percent Threshold	Threshold for Empty Bucket Percent that indicates the number of empty buckets in the hash index.	10
Enabled	Enables or disables the workflow.	Yes
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.	43200
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
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.DBFilegroupFx

Parent Monitor

System.Health.ConfigurationState

Category

ConfigurationHealth

Enabled

True

Alert Generate

True

Alert Severity

Warning

Alert Priority

Normal

Alert Auto Resolve

True

Monitor Type

Microsoft.SQLServer.Linux.MonitorType.DBFilegroupFx.HashIndexAvgChainLength

Remotable

True

Accessibility

Public

Alert Message

MSSQL on Linux: Average length of the row chains in the hash buckets is too long

Database "{2}" on SQL Server instance "{1}", computer "{0}" has tables with indexes that contain too many duplicates. The usage of a NONCLUSTERED index would be more appropriate. {3}

RunAs

Default

Source Code:

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

  <Category>ConfigurationHealth</Category>

  <AlertSettings AlertMessage="Microsoft.SQLServer.Linux.Monitor.DBFilegroupFx.HashIndexAvgChainLength.AlertMessage">

    <AlertOnState>Warning</AlertOnState>

    <AutoResolve>true</AutoResolve>

    <AlertPriority>Normal</AlertPriority>

    <AlertSeverity>Warning</AlertSeverity>

    <AlertParameters>

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

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

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

      <AlertParameter4>$Data/Context/Property[@Name='Status']$</AlertParameter4>

    </AlertParameters>

  </AlertSettings>

  <OperationalStates>

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

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

  </OperationalStates>

  <Configuration>

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

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

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

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

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

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

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

    <IntervalSeconds>43200</IntervalSeconds>

    <SyncTime/>

    <SqlExecTimeoutSeconds>60</SqlExecTimeoutSeconds>

    <SqlTimeoutSeconds>15</SqlTimeoutSeconds>

    <TimeoutSeconds>300</TimeoutSeconds>

    <EmptyBucketPercentThreshold>10</EmptyBucketPercentThreshold>

    <AvgChainLengthThreshold>100</AvgChainLengthThreshold>

    <ErrorTopLines>5</ErrorTopLines>

  </Configuration>

</UnitMonitor>