functions/Test-DbaMaxMemory.ps1

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Function Test-DbaMaxMemory {
<#
.SYNOPSIS
Calculates the recommended value for SQL Server 'Max Server Memory' configuration setting. Works on SQL Server 2000-2014.
 
.DESCRIPTION
Inspired by Jonathan Kehayias's post about SQL Server Max memory (http://bit.ly/sqlmemcalc), this script displays a SQL Server's:
total memory, currently configured SQL max memory, and the calculated recommendation.
 
Jonathan notes that the formula used provides a *general recommendation* that doesn't account for everything that may be going on in your specific environment.
 
.PARAMETER SqlInstance
Allows you to specify a comma separated list of servers to query.
 
.PARAMETER SqlCredential
Allows you to login to servers using SQL Logins as opposed to Windows Auth/Integrated/Trusted. To use:
 
$cred = Get-Credential, then pass $cred variable to this parameter.
 
Windows Authentication will be used when SqlCredential is not specified. To connect as a different Windows user, run PowerShell as that user.    
 
.PARAMETER Silent
Use this switch to disable any kind of verbose messages
 
.NOTES
Tags: Memory
dbatools PowerShell module (https://dbatools.io, clemaire@gmail.com)
Copyright (C) 2016 Chrissy LeMaire
 
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
 
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.
 
.LINK
https://dbatools.io/Test-DbaMaxMemory
 
.EXAMPLE
Test-DbaMaxMemory -SqlInstance sqlcluster,sqlserver2012
 
Calculate the 'Max Server Memory' settings for all servers within the SQL Server Central Management Server "sqlcluster"
 
.EXAMPLE
Test-DbaMaxMemory -SqlInstance sqlcluster | Where-Object { $_.SqlMaxMB -gt $_.TotalMB } | Set-DbaMaxMemory
 
Find all servers in CMS that have Max SQL memory set to higher than the total memory of the server (think 2147483647) and set it to recommended value.
 
#>

    [CmdletBinding()]
    param (
        [parameter(Position = 0, Mandatory = $true, ValueFromPipeline = $True)]
        [Alias("ServerInstance", "SqlServer", "SqlServers")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [switch]$Silent
    )
    
    process {
        foreach ($instance in $SqlInstance) {
            Write-Message -Level Verbose -Message "Counting the running SQL Server instances on $instance"
            
            try {
                # Get number of instances running
                $ipaddr = Resolve-SqlIpAddress -SqlInstance $instance
                $sqlservices = Get-Service -ComputerName $ipaddr | Where-Object { $_.DisplayName -like 'SQL Server (*' -and $_.Status -eq 'Running' }
                $instancecount = $sqlservices.count
            }
            catch {
                Write-Message -Level Warning -Message "Couldn't get accurate SQL Server instance count on $instance. Defaulting to 1."
                $instancecount = 1
            }
            
            $server = Get-DbaMaxMemory -SqlInstance $instance -SqlCredential $SqlCredential
            
            if ($null -eq $server) {
                continue
            }
            $reserve = 1
            
            $maxmemory = $server.SqlMaxMB
            $totalmemory = $server.TotalMB
            
            if ($totalmemory -ge 4096) {
                $currentCount = $totalmemory
                while ($currentCount/4096 -gt 0) {
                    if ($currentCount -gt 16384) {
                        $reserve += 1
                        $currentCount += -8192
                    }
                    else {
                        $reserve += 1
                        $currentCount += -4096
                    }
                }
                $recommendedMax = [int]($totalmemory - ($reserve * 1024))
            }
            else {
                $recommendedMax = $totalmemory * .5
            }
            
            $recommendedMax = $recommendedMax/$instancecount
            
            [pscustomobject]@{
                Server   = $server.Server
                ComputerName = $server.ComputerName
                InstanceName = $server.InstanceName
                SqlInstance = $server.SqlInstance
                InstanceCount = $instancecount
                TotalMB  = [int]$totalmemory
                SqlMaxMB = [int]$maxmemory
                RecommendedMB = [int]$recommendedMax
            } | Select-DefaultView -ExcludeProperty Server
        }
    }
}