functions/Get-DbaDbExtentDiff.ps1

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function Get-DbaDbExtentDiff {
    <#
    .SYNOPSIS
        What percentage of a database has changed since the last full backup
 
    .DESCRIPTION
        This is only an implementation of the script created by Paul S. Randal to find what percentage of a database has changed since the last full backup.
        https://www.sqlskills.com/blogs/paul/new-script-how-much-of-the-database-has-changed-since-the-last-full-backup/
 
    .PARAMETER SqlInstance
        The target SQL Server instance
 
    .PARAMETER SqlCredential
        Login to the target instance using alternative credentials. Windows and SQL Authentication supported. Accepts credential objects (Get-Credential)
 
    .PARAMETER Database
        The database(s) to process - this list is auto-populated from the server. If unspecified, all databases will be processed.
 
    .PARAMETER ExcludeDatabase
        The database(s) to exclude - this list is auto-populated from the server
 
    .PARAMETER WhatIf
        Shows what would happen if the command were to run. No actions are actually performed.
 
    .PARAMETER Confirm
        Prompts you for confirmation before executing any changing operations within the command.
 
    .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: Backup, Database
        Author: Viorel Ciucu, cviorel.com
 
        Website: https://dbatools.io
        Copyright: (c) 2018 by dbatools, licensed under MIT
        License: GNU GPL v3 https://opensource.org/licenses/GPL-3.0
 
    .LINK
        http://dbatools.io/Get-DbaDbExtentDiff
 
    .EXAMPLE
        PS C:\> Get-DbaDbExtentDiff -SqlInstance SQL2016 -Database DBA
 
        Get the changes for the DBA database.
 
    .EXAMPLE
        PS C:\> $Cred = Get-Credential sqladmin
        PS C:\> Get-DbaDbExtentDiff -SqlInstance SQL2017N1, SQL2017N2, SQL2016 -Database DB01 -SqlCredential $Cred
 
        Get the changes for the DB01 database on multiple servers.
 
    #>

    [CmdletBinding()]
    param (
        [parameter(Mandatory, ValueFromPipeline)]
        [Alias('ServerInstance', 'SqlServer')]
        [DbaInstance[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [object[]]$Database,
        [object[]]$ExcludeDatabase,
        [switch]$EnableException
    )

    begin {
        $rex = [regex]':(?<extent>[\d]+)\)'
        function Get-DbaExtent ([string[]]$field) {
            $res = 0
            foreach ($f in $field) {
                $extents = $rex.Matches($f)
                if ($extents.Count -eq 1) {
                    $res += 1
                } else {
                    $pages = [int]$extents[1].Groups['extent'].Value - [int]$extents[0].Groups['extent'].Value
                    $res += $pages / 8 + 1
                }
            }
            return $res
        }
    }

    process {

        foreach ($instance in $SqlInstance) {
            try {
                $server = Connect-SqlInstance -SqlInstance $instance -SqlCredential $SqlCredential -NonPooled
            } catch {
                Stop-Function -Message "Error occurred while establishing connection to $instance" -Category ConnectionError -ErrorRecord $_ -Target $instance -Continue
            }

            $dbs = $server.Databases

            if ($Database) {
                $dbs = $dbs | Where-Object Name -In $Database
            }

            if ($ExcludeDatabase) {
                $dbs = $dbs | Where-Object Name -NotIn $ExcludeDatabase
            }

            $sourcedbs = @()
            foreach ($db in $dbs) {
                if ($db.IsAccessible -ne $true) {
                    Write-Message -Level Verbose -Message "$db is not accessible on $instance, skipping"
                } else {
                    $sourcedbs += $db
                }
            }

            #Available from 2016 SP2
            if ($server.Version -ge [version]'13.0.5026') {
                foreach ($db in $sourcedbs) {
                    $DBCCPageQueryDMV = "
                        SELECT
                        SUM(total_page_count) / 8 as [ExtentsTotal],
                        SUM(modified_extent_page_count) / 8 as [ExtentsChanged],
                        100.0 * SUM(modified_extent_page_count)/SUM(total_page_count) as [ChangedPerc]
                        FROM sys.dm_db_file_space_usage
                    "

                    $DBCCPageResults = $server.Query($DBCCPageQueryDMV, $db.Name)
                    [pscustomobject]@{
                        ComputerName   = $server.ComputerName
                        InstanceName   = $server.ServiceName
                        SqlInstance    = $server.DomainInstanceName
                        DatabaseName   = $db.Name
                        ExtentsTotal   = $DBCCPageResults.ExtentsTotal
                        ExtentsChanged = $DBCCPageResults.ExtentsChanged
                        ChangedPerc    = [math]::Round($DBCCPageResults.ChangedPerc, 2)
                    }
                }
            } else {
                $MasterFilesQuery = "
                        SELECT [file_id], [size], database_id, db_name(database_id) as dbname FROM master.sys.master_files
                        WHERE [type_desc] = N'ROWS'
                    "

                $MasterFiles = $server.Query($MasterFilesQuery)
                $MasterFiles = $MasterFiles | Where-Object dbname -In $sourcedbs.Name
                $MasterFilesGrouped = $MasterFiles | Group-Object -Property dbname

                foreach ($db in $MasterFilesGrouped) {
                    $sizeTotal = 0
                    $dbExtents = @()
                    foreach ($results in $db.Group) {
                        $extentID = 0
                        $sizeTotal = $sizeTotal + $results.size / 8
                        while ($extentID -lt $results.size) {
                            $pageID = $extentID + 6
                            $DBCCPageQuery = "DBCC PAGE ('$($results.dbname)', $($results.file_id), $pageID, 3) WITH TABLERESULTS, NO_INFOMSGS"
                            $DBCCPageResults = $server.Query($DBCCPageQuery)
                            $dbExtents += $DBCCPageResults | Where-Object { $_.VALUE -eq ' CHANGED' -And $_.ParentObject -like 'DIFF_MAP*'}
                            $extentID = $extentID + 511232
                        }
                    }
                    $extents = Get-DbaExtent $dbExtents.Field
                    [pscustomobject]@{
                        ComputerName   = $server.ComputerName
                        InstanceName   = $server.ServiceName
                        SqlInstance    = $server.DomainInstanceName
                        DatabaseName   = $db.Name
                        ExtentsTotal   = $sizeTotal
                        ExtentsChanged = $extents
                        ChangedPerc    = [math]::Round(($extents / $sizeTotal * 100), 2)
                    }
                }
            }
        }
    }
}