functions/Test-DbaMaxDop.ps1

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function Test-DbaMaxDop {
    <#
  .SYNOPSIS
   Displays information relating to SQL Server Max Degree of Parallelism setting. Works on SQL Server 2005-2016.
 
  .DESCRIPTION
   Inspired by Sakthivel Chidambaram's post about SQL Server MAXDOP Calculator (https://blogs.msdn.microsoft.com/sqlsakthi/p/maxdop-calculator-SqlInstance/),
   this script displays a SQL Server's: max dop configured, and the calculated recommendation.
 
   For SQL Server 2016 shows:
    - Instance max dop configured and the calculated recommendation
    - max dop configured per database (new feature)
 
   More info:
    https://support.microsoft.com/en-us/kb/2806535
    https://blogs.msdn.microsoft.com/sqlsakthi/2012/05/23/wow-we-have-maxdop-calculator-for-sql-server-it-makes-my-job-easier/
 
   These are just general recommendations for SQL Server and are a good starting point for setting the "max degree of parallelism" option.
 
   .PARAMETER SqlInstance
   The SQL Server instance(s) to connect to.
 
        .PARAMETER SqlCredential
   Allows you to login to servers using SQL Logins instead of Windows Authentication (AKA Integrated or Trusted). To use:
 
   $scred = Get-Credential, then pass $scred object to the -SqlCredential parameter.
 
   Windows Authentication will be used if SqlCredential is not specified. SQL Server does not accept Windows credentials being passed as credentials.
 
   To connect as a different Windows user, run PowerShell as that user.
 
  .PARAMETER Detailed
   If this switch is enabled, detailed information related to MaxDop settings is returned.
 
  .PARAMETER EnableException
   By default, when something goes wrong we try to catch it, interpret it and give you a friendly warning message.
   This avoids overwhelming you with "sea of red" exceptions, but is inconvenient because it basically disables advanced scripting.
   Using this switch turns this "nice by default" feature off and enables you to catch exceptions with your own try/catch.
 
  .NOTES
   Tags: MaxDop, SPConfigure
   Author : Claudio Silva (@claudioessilva)
   Requires: sysadmin access on SQL Servers
 
   dbatools PowerShell module (https://dbatools.io, clemaire@gmail.com)
   Copyright (C) 2016 Chrissy LeMaire
            License: GNU GPL v3 https://opensource.org/licenses/GPL-3.0
 
  .LINK
   https://dbatools.io/Test-DbaMaxDop
 
  .EXAMPLE
   Test-DbaMaxDop -SqlInstance sql2008, sqlserver2012
 
   Get Max DOP setting for servers sql2008 and sqlserver2012 and also the recommended one.
 
  .EXAMPLE
   Test-DbaMaxDop -SqlInstance sql2014 -Detailed
 
   Shows Max DOP setting for server sql2014 with the recommended value. As the -Detailed switch was used will also show the 'NUMANodes' and 'NumberOfCores' of each instance
 
  .EXAMPLE
   Test-DbaMaxDop -SqlInstance sqlserver2016 -Detailed
 
   Get Max DOP setting for servers sql2016 with the recommended value. As the -Detailed switch was used will also show the 'NUMANodes' and 'NumberOfCores' of each instance. Because it is an 2016 instance will be shown 'InstanceVersion', 'Database' and 'DatabaseMaxDop' columns.
 #>

    [CmdletBinding()]
    param (
        [parameter(Position = 0, Mandatory = $true, ValueFromPipeline = $True)]
        [Alias("ServerInstance", "SqlServer", "SqlServers")]
        [DbaInstance[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [Switch]$Detailed,
        [switch][Alias('Silent')]$EnableException
    )

    begin {
        Test-DbaDeprecation -DeprecatedOn 1.0.0 -Parameter Detailed

        $notesDopLT = "Before changing MaxDop, consider that the lower value may have been intentionally set."
        $notesDopGT = "Before changing MaxDop, consider that the higher value may have been intentionally set."
        $notesDopZero = "This is the default setting. Consider using the recommended value instead."
        $notesDopOne = "Some applications like SharePoint, Dynamics NAV, SAP, BizTalk has the need to use MAXDOP = 1. Please confirm that your instance is not supporting one of these applications prior to changing the MaxDop."
        $notesAsRecommended = "Configuration is as recommended."
        $collection = @()
    }

    process {
        $hasScopedConfig = $false

        foreach ($instance in $SqlInstance) {
            try {
                Write-Message -Level Verbose -Message "Connecting to $instance"
                $server = Connect-SqlInstance -SqlInstance $instance -SqlCredential $SqlCredential -MinimumVersion 9
            }
            catch {
                Stop-Function -Message "Failure" -Category ConnectionError -ErrorRecord $_ -Target $instance -Continue
            }

            #Get current configured value
            $maxDop = $server.Configuration.MaxDegreeOfParallelism.ConfigValue

            try {
                #represents the Number of NUMA nodes
                $sql = "SELECT COUNT(DISTINCT memory_node_id) AS NUMA_Nodes FROM sys.dm_os_memory_clerks WHERE memory_node_id!=64"
                $numaNodes = $server.ConnectionContext.ExecuteScalar($sql)
            }
            catch {
                Stop-Function -Message "Failed to get Numa node count." -ErrorRecord $_ -Target $server -Continue
            }

            try {
                #represents the Number of Processor Cores
                $sql = "SELECT COUNT(scheduler_id) FROM sys.dm_os_schedulers WHERE status = 'VISIBLE ONLINE'"
                $numberOfCores = $server.ConnectionContext.ExecuteScalar($sql)
            }
            catch {
                Stop-Function -Message "Failed to get number of cores." -ErrorRecord $_ -Target $server -Continue
            }

            #Calculate Recommended Max Dop to instance
            #Server with single NUMA node
            if ($numaNodes -eq 1) {
                if ($numberOfCores -lt 8) {
                    #Less than 8 logical processors    - Keep MAXDOP at or below # of logical processors
                    $recommendedMaxDop = $numberOfCores
                }
                else {
                    #Equal or greater than 8 logical processors - Keep MAXDOP at 8
                    $recommendedMaxDop = 8
                }
            }
            else {
                #Server with multiple NUMA nodes
                if (($numberOfCores / $numaNodes) -lt 8) {
                    # Less than 8 logical processors per NUMA node - Keep MAXDOP at or below # of logical processors per NUMA node
                    $recommendedMaxDop = [int]($numberOfCores / $numaNodes)
                }
                else {
                    # Greater than 8 logical processors per NUMA node - Keep MAXDOP at 8
                    $recommendedMaxDop = 8
                }
            }

            #Setting notes for instance max dop value
            $notes = $null
            if ($maxDop -eq 1) {
                $notes = $notesDopOne
            }
            else {
                if ($maxDop -ne 0 -and $maxDop -lt $recommendedMaxDop) {
                    $notes = $notesDopLT
                }
                else {
                    if ($maxDop -ne 0 -and $maxDop -gt $recommendedMaxDop) {
                        $notes = $notesDopGT
                    }
                    else {
                        if ($maxDop -eq 0) {
                            $notes = $notesDopZero
                        }
                        else {
                            $notes = $notesAsRecommended
                        }
                    }
                }
            }

            $collection += [pscustomobject]@{
                ComputerName          = $server.NetName
                InstanceName          = $server.ServiceName
                SqlInstance           = $server.DomainInstanceName
                InstanceVersion       = $server.Version
                Database              = "N/A"
                DatabaseMaxDop        = "N/A"
                CurrentInstanceMaxDop = $maxDop
                RecommendedMaxDop     = $recommendedMaxDop
                NUMANodes             = $numaNodes
                NumberOfCores         = $numberOfCores
                Notes                 = $notes
            }

            # On SQL Server 2016 and higher, MaxDop can be set on a per-database level
            if ($server.VersionMajor -ge 13) {
                $hasScopedConfig = $true
                Write-Message -Level Verbose -Message "SQL Server 2016 or higher detected, checking each database's MaxDop."

                $databases = $server.Databases | where-object {$_.IsSystemObject -eq $false}

                foreach ($database in $databases) {
                    if ($database.IsAccessible -eq $false) {
                        Write-Message -Level Verbose -Message "Database $database is not accessible."
                        continue
                    }
                    Write-Message -Level Verbose -Message "Checking database '$($database.Name)'."

                    $dbmaxdop = $database.MaxDop

                    $collection += [pscustomobject]@{
                        ComputerName          = $server.NetName
                        InstanceName          = $server.ServiceName
                        SqlInstance           = $server.DomainInstanceName
                        InstanceVersion       = $server.Version
                        Database              = $database.Name
                        DatabaseMaxDop        = $dbmaxdop
                        CurrentInstanceMaxDop = $maxDop
                        RecommendedMaxDop     = $recommendedMaxDop
                        NUMANodes             = $numaNodes
                        NumberOfCores         = $numberOfCores
                        Notes                 = if ($dbmaxdop -eq 0) { "Will use CurrentInstanceMaxDop value" } else { "$notes" }
                    }
                }
            }
            Select-DefaultView -InputObject $collection -Property ComputerName, InstanceName, SqlInstance, Database, DatabaseMaxDop, CurrentInstanceMaxDop, RecommendedMaxDop, Notes
        }
    }
}