functions/Restore-DbaFromDatabaseSnapshot.ps1

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#ValidationTags#FlowControl#
function Restore-DbaFromDatabaseSnapshot {
    <#
.SYNOPSIS
Restores databases from snapshots
 
.DESCRIPTION
Restores the database from the snapshot, discarding every modification made to the database
NB: Restoring to a snapshot will result in every other snapshot of the same database to be dropped
It also fixes some long-standing bugs in SQL Server when restoring from snapshots
 
.PARAMETER SqlInstance
The SQL Server that you're connecting to
 
.PARAMETER SqlCredential
Credential object used to connect to the SQL Server as a different user
 
.PARAMETER Database
Restores from the last snapshot databases with this names only. You can pass either Databases or Snapshots
 
.PARAMETER ExcludeDatabase
The database(s) to exclude - this list is auto-populated from the server
 
.PARAMETER Snapshot
Restores databases from snapshots with this names only. You can pass either Databases or Snapshots
 
.PARAMETER Force
If restoring from a snapshot involves dropping any other shapshot, you need to explicitly
use -Force to let this command delete the ones not involved in the restore process.
Also, -Force will forcibly kill all running queries that prevent the restore process.
 
.PARAMETER WhatIf
Shows what would happen if the command were to run
 
.PARAMETER Confirm
Prompts for confirmation of every step.
 
.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: DisasterRecovery, Snapshot, Backup, Restore, Database
Author: niphlod
 
Website: https://dbatools.io
Copyright: (C) Chrissy LeMaire, clemaire@gmail.com
License: GNU GPL v3 https://opensource.org/licenses/GPL-3.0
 
.LINK
 https://dbatools.io/Restore-DbaFromDatabaseSnapshot
 
.EXAMPLE
Restore-DbaFromDatabaseSnapshot -SqlInstance sqlserver2014a -Database HR, Accounting
 
Restores HR and Accounting databases using the latest snapshot available
 
.EXAMPLE
Restore-DbaFromDatabaseSnapshot -SqlInstance sqlserver2014a -Snapshot HR_snap_20161201, Accounting_snap_20161101
 
Restores databases from snapshots named HR_snap_20161201 and Accounting_snap_20161101
 
#>

    [CmdletBinding(SupportsShouldProcess = $true)]
    Param (
        [parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [Alias("ServerInstance", "SqlServer")]
        [DbaInstanceParameter[]]$SqlInstance,
        [Alias("Credential")]
        [PSCredential]
        $SqlCredential,
        [Alias("Databases")]
        [object[]]$Database,
        [object[]]$ExcludeDatabase,
        [object[]]$Snapshot,
        [switch]$Force,
        [switch][Alias('Silent')]$EnableException
    )

    process {
        if (!$Snapshot -and !$Database -and !$ExcludeDatabase) {
            Stop-Function -Message "You must specify either -Snapshot (to restore from) or -Database/-ExcludeDatabase (to restore to)"
        }

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

            $alldbs = $server.Databases

            # vault to hold all programmed operations from --> to
            $operations = @()

            if (!$Snapshot -and !$Database -and !$ExcludeDatabase) {
                # Restore all databases from the latest snapshot
                Write-Message -Level Verbose -Message "Selected all databases"
                $dbs = $alldbs | Where-Object IsDatabaseSnapshot -eq $true
            }
            elseif ($Database) {
                # Restore only these databases from their latest snapshot
                Write-Message -Level Verbose -Message "Selected only databases"
                $dbs = $alldbs | Where-Object { $Database -contains $_.DatabaseSnapshotBaseName }
            }
            elseif ($ExcludeDatabase) {
                Write-Message -Level Verbose -Message "Excluded only databases"
                $dbs = $alldbs | Where-Object { $ExcludeDatabase -notcontains $_.DatabaseSnapshotBaseName }
            }
            elseif ($Snapshot) {
                # Restore databases from these snapshots
                Write-Message -Level Verbose -Message "Selected only snapshots"
                $dbs = $alldbs | Where-Object { $Snapshot -contains $_.Name }
                $basedatabases = $dbs | Select-Object -ExpandProperty DatabaseSnapshotBaseName | Get-Unique
                if ($basedatabases.count -ne $Snapshot.count -and $dbs.Count -ne 0) {
                    Write-Message -Level Warning -Message "Multiple snapshots selected for the same database, skipping"
                    continue
                }
            }

            $opshash = @{ }

            foreach ($db in $dbs) {
                if ($db.DatabaseSnapshotBaseName -notin $opshash.Keys) {
                    if ($snapshot.count -gt 0) {
                        # just in the need to drop every other snapshot
                        $todrop = $alldbs | Where-Object { $_.DatabaseSnapshotBaseName -eq $db.DatabaseSnapshotBaseName }
                        $todrop = $todrop | Select-Object Name
                        $opshash[$db.DatabaseSnapshotBaseName] = @{
                            'from' = $db | Select-Object Name, DatabaseSnapshotBaseName, CreateDate
                            'drop' = $todrop
                        }
                    }
                    else {
                        $opshash[$db.DatabaseSnapshotBaseName] = @{
                            'from' = $db
                            'drop' = @()
                        }
                    }
                }
                else {
                    # store each older snapshot in the drop list while enumerating
                    if ($db.createDate -gt $opshash[$db.DatabaseSnapshotBaseName]['from'].CreateDate) {
                        $prev = $opshash[$db.DatabaseSnapshotBaseName]['from']
                        $opshash[$db.DatabaseSnapshotBaseName]['from'] = $db | Select-Object Name, DatabaseSnapshotBaseName, CreateDate
                        $opshash[$db.DatabaseSnapshotBaseName]['drop'] += $prev
                    }
                }
            }
            foreach ($dbname in $opshash.Keys) {
                $drop = @()
                foreach ($todrop in $opshash[$dbname]['drop']) {
                    $drop += $todrop.Name
                }
                $operations += @{
                    'from' = $opshash[$dbname]['from'].Name
                    'to'   = $dbname
                    'drop' = $drop
                }
            }

            foreach ($op in $operations) {
                # Check if there are FS, because then a restore is not possible
                $all_FS = $server.Databases[$op['to']].FileGroups | Where-Object FileGroupType -eq 'FileStreamDataFileGroup'
                if ($all_FS.Count -gt 0) {
                    Write-Message -Level Warning -Message "Database $($op['to']) has FileStream group(s). You cannot restore from snapshots"
                    [PSCustomObject]@{
                        ComputerName = $server.NetName
                        InstanceName = $server.ServiceName
                        SqlInstance  = $server.DomainInstanceName
                        Database     = $op['to']
                        Snapshot     = $op['from']
                        Status       = 'Error'
                        Notes        = "Database $($op['to']) has FileStream group(s). You cannot restore from snapshots"
                    }
                    break
                }
                # Get log size and autogrowth
                $orig_logproperties = $server.Databases[$op['to']].LogFiles | Select-Object id, size
                # Drop what needs to be dropped
                $operror = $false

                if ($op['drop'].count -gt 1 -and $Force -eq $false) {
                    $warnmsg = @()
                    $warnmsg += "The restore process for $($op['to']) from $($op['from']) needs to drop the following:"
                    foreach ($db in $op['drop']) {
                        $warnmsg += $db
                    }
                    $warnmsg += "Use -Force if you really want to drop these snapshots."
                    Write-Message -Level Warning -Message ($warnmsg -join "`n")
                    break
                }
                foreach ($drop in $op['drop']) {
                    If ($Pscmdlet.ShouldProcess($server.name, "Remove db snapshot $drop")) {
                        # skip it if it's the same name
                        if ($drop -ne $($op['from'])) {
                            try {
                                if ($Force) {
                                    # snapshot with open transactions cannot be dropped
                                    $server.KillAllProcesses($drop)
                                }
                                $null = $server.Query("USE master; DROP DATABASE [$drop]")
                                $status = "Dropped"
                            } catch {
                                Write-Message -Level Warning -Message $_
                                $operror = $true
                                break
                            }
                        }
                    }
                }
                if ($operror) {
                    Write-Message -Level Warning -Message "Errors trying to restore $($op['to']) from $($op['from'])"
                    [PSCustomObject]@{
                        ComputerName = $server.NetName
                        InstanceName = $server.ServiceName
                        SqlInstance  = $server.DomainInstanceName
                        Database     = $op['to']
                        Snapshot     = $op['from']
                        Status       = 'Error'
                        Notes        = "Failed to drop some snapshots"
                    }
                    break
                }

                # Need a proper restore now
                if ($Pscmdlet.ShouldProcess($server.DomainInstanceName, "Restore db $($op['to']) from $($op['from'])")) {
                    $query = "USE master; RESTORE DATABASE [$($op['to'])] FROM DATABASE_SNAPSHOT='$($op['from'])'"
                    try {
                        if ($Force) {
                            # for whatever reason, a snapshot with open transactions, albeit read-only, block the restore process
                            $server.KillAllProcesses($op['from'])
                            # for a "good" reason, all open transactions on the destination block the restore process
                            $server.KillAllProcesses($op['to'])
                        }
                        $null = $server.Query($query)
                    }
                    catch {
                        $operror = $true
                        $inner = $_.Exception.Message
                        Stop-Function -Message "Original exception: $inner, Query issued: $query, Error: $_.Exception.InnerException.InnerException.Message" -ErrorRecord $_
                    }
                }
                if ($operror) {
                    Write-Message -Level Warning -Message "Errors trying to restore $($op['to']) from $($op['from'])"
                    [PSCustomObject]@{
                        ComputerName = $server.NetName
                        InstanceName = $server.ServiceName
                        SqlInstance  = $server.DomainInstanceName
                        Database     = $op['to']
                        Snapshot     = $op['from']
                        Status       = 'Error'
                        Notes        = ''
                    }
                    break
                }
                # Comparing sizes before and after, need to reconnect to see if size
                # changed
                $server = Connect-SqlInstance -SqlInstance $instance -SqlCredential $SqlCredential
                foreach ($log in $server.Databases[$op['to']].LogFiles) {
                    $matching = $orig_logproperties | Where-Object ID -eq $log.ID
                    if ($matching.Size -ne $log.Size) {
                        Write-Message -Level Verbose -Message "Resizing log to the original value"
                        $log.Size = $matching.Size
                        $log.Alter()
                    }
                }
                [PSCustomObject]@{
                    ComputerName = $server.NetName
                    InstanceName = $server.ServiceName
                    SqlInstance  = $server.DomainInstanceName
                    Database     = $op['to']
                    Snapshot     = $op['from']
                    Status       = 'Restored'
                    Notes        = 'Remember to take a backup now, and also to remove the snapshot if not needed'
                }
            }
        }
    }
}