functions/Clear-DbaPlanCache.ps1

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function Clear-DbaPlanCache {
    <#
    .SYNOPSIS
        Removes ad-hoc and prepared plan caches is single use plans are over defined threshold.
 
    .DESCRIPTION
        Checks ad-hoc and prepared plan cache for each database, if over 100 MBs removes from the cache.
 
        This command automates that process.
 
        References: https://www.sqlskills.com/blogs/kimberly/plan-cache-adhoc-workloads-and-clearing-the-single-use-plan-cache-bloat/
 
    .PARAMETER SqlInstance
        The target SQL Server instance or instances.
 
    .PARAMETER SqlCredential
        Login to the target instance using alternative credentials. Windows and SQL Authentication supported. Accepts credential objects (Get-Credential)
 
    .PARAMETER Threshold
        Memory used threshold.
 
    .PARAMETER InputObject
        Enables results to be piped in from Get-DbaPlanCache.
 
    .PARAMETER WhatIf
        If this switch is enabled, no actions are performed but informational messages will be displayed that explain what would happen if the command were to run.
 
    .PARAMETER Confirm
        If this switch is enabled, you will be prompted for confirmation before executing any operations that change state.
 
    .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: Memory
        Author: Tracy Boggiano, databasesuperhero.com
 
        Website: https://dbatools.io
        Copyright: (c) 2018 by dbatools, licensed under MIT
        License: MIT https://opensource.org/licenses/MIT
 
    .LINK
        https://dbatools.io/Clear-DbaPlanCache
 
    .EXAMPLE
        PS C:\> Clear-DbaPlanCache -SqlInstance sql2017 -Threshold 200
 
        Logs into the SQL Server instance "sql2017" and removes plan caches if over 200 MB.
 
    .EXAMPLE
        PS C:\> Clear-DbaPlanCache -SqlInstance sql2017 -SqlCredential sqladmin
 
        Logs into the SQL instance using the SQL Login 'sqladmin' and then Windows instance as 'ad\sqldba'
        and removes if Threshold over 100 MB.
 
    .EXAMPLE
        PS C:\> Find-DbaInstance -ComputerName localhost | Get-DbaPlanCache | Clear-DbaPlanCache -Threshold 200
 
        Scans localhost for instances using the browser service, traverses all instances and gets the plan cache for each, clears them out if they are above 200 MB.
    #>

    [CmdletBinding(SupportsShouldProcess)]
    param (
        [Alias("ServerInstance", "SqlServer", "SqlServers")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [int]$Threshold = 100,
        [parameter(ValueFromPipeline)]
        [object[]]$InputObject,
        [switch]$EnableException
    )
    process {
        foreach ($instance in $SqlInstance) {
            $InputObject += Get-DbaPlanCache -SqlInstance $instance -SqlCredential $SqlCredential
        }

        foreach ($result in $InputObject) {
            if ($result.MB -ge $Threshold) {
                if ($Pscmdlet.ShouldProcess($($result.SqlInstance), "Cleared SQL Plans plan cache")) {
                    try {
                        $server = Connect-SqlInstance -SqlInstance $result.SqlInstance -SqlCredential $SqlCredential
                    } catch {
                        Stop-Function -Message "Failure" -Category ConnectionError -ErrorRecord $_ -Target $instance -Continue
                    }

                    $server.Query("DBCC FREESYSTEMCACHE('SQL Plans')")
                    [PSCustomObject]@{
                        ComputerName = $result.ComputerName
                        InstanceName = $result.InstanceName
                        SqlInstance  = $result.SqlInstance
                        Size         = $result.Size
                        Status       = "Plan cache cleared"
                    }
                }
            } else {
                if ($Pscmdlet.ShouldProcess($($result.SqlInstance), "Results $($result.Size) below threshold")) {
                    [PSCustomObject]@{
                        ComputerName = $result.ComputerName
                        InstanceName = $result.InstanceName
                        SqlInstance  = $result.SqlInstance
                        Size         = $result.Size
                        Status       = "Plan cache size below threshold ($Threshold) "
                    }
                    Write-Message -Level Verbose -Message "Plan cache size below threshold ($Threshold) "
                }
            }
        }
    }
}