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.

THIS CODE IS PROVIDED "AS IS", WITH NO WARRANTIES.

.PARAMETER SqlServer
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.    

.NOTES
Author : Chrissy LeMaire (@cl), netnerds.net
Requires: sysadmin access on SQL Servers

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/Get-DbaMaxMemoryory

.EXAMPLE
Test-DbaMaxMemory -SqlServer sqlcluster,sqlserver2012

Calculate the 'Max Server Memory' settings for all servers within the SQL Server Central Management Server "sqlcluster"

.EXAMPLE
Test-DbaMaxMemory -SqlServer 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 = $True)]
        [Alias("ServerInstance", "SqlInstance", "SqlServers")]
        [object]$SqlServer,
        [System.Management.Automation.PSCredential]$SqlCredential
    )
    
    PROCESS
    {
        foreach ($servername in $sqlserver)
        {
            Write-Verbose "Counting the running SQL Server instances on $servername"

            try
            {
                # Get number of instances running
                $ipaddr = Resolve-SqlIpAddress -SqlServer $servername
                $sqls = Get-Service -ComputerName $ipaddr | Where-Object { $_.DisplayName -like 'SQL Server (*' -and $_.Status -eq 'Running' }
                $sqlcount = $sqls.count
            }
            catch
            {
                Write-Warning "Couldn't get accurate SQL Server instance count on $servername. Defaulting to 1."
                $sqlcount = 1
            }
            

            $server = Get-DbaMaxMemory -SqlServer $servername -SqlCredential $SqlCredential
            
            if($server -eq $null)
            {
                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 = $recommendedMax/$sqlcount
            
            [pscustomobject]@{
                Server = $server.Server
                InstanceCount = $sqlcount
                TotalMB = $totalmemory
                SqlMaxMB = $maxmemory
                RecommendedMB = $recommendedMax
            }
        }
    }
}