functions/Find-DbaUnusedIndex.ps1

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function Find-DbaUnusedIndex {
    <#
  .SYNOPSIS
   Find Unused indexes
 
  .DESCRIPTION
   This command will help you to find Unused indexes on a database or a list of databases
 
   Also tells how much space you can save by dropping the index.
   We show the type of compression so you can make a more considered decision.
   For now only supported for CLUSTERED and NONCLUSTERED indexes
 
   You can select the indexes you want to drop on the gridview and by click OK the drop statement will be generated.
 
  .PARAMETER SqlInstance
   The SQL Server instance.
 
  .PARAMETER SqlCredential
   Allows you to login to servers using SQL Logins as opposed to Windows Auth/Integrated/Trusted. To use:
 
   $scred = Get-Credential, then pass $scred object to the -SqlCredential parameter.
 
   Windows Authentication will be used if SqlCredential is not specified. SQL Server does not accept Windows credentials being passed as credentials. To connect as a different Windows user, run PowerShell as that user.
 
  .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 FilePath
   The filepath of the file to write to.
 
  .PARAMETER NoClobber
   Do not overwrite file
 
  .PARAMETER Append
   Append to file
 
  .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 Silent
   Use this switch to disable any kind of verbose messages
 
  .NOTES
   Tags: Indexes
   Original Author: Aaron Nelson (@SQLvariant), SQLvariant.com
 
   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/Find-DbaUnusedIndex
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sql2005 -FilePath C:\temp\sql2005-UnusedIndexes.sql
 
   Exports SQL for the Unused indexes in server "sql2005" chosen on grid-view and writes them to the file "C:\temp\sql2005-UnusedIndexes.sql"
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sql2005 -FilePath C:\temp\sql2005-UnusedIndexes.sql -Append
 
   Exports SQL for the Unused indexes in server "sql2005" chosen on grid-view and writes/appends them to the file "C:\temp\sql2005-UnusedIndexes.sql"
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sqlserver2016 -SqlCredential $cred
 
   Will find exact Unused indexes on all user databases present on sqlserver2016 will be verified using SQL credentials.
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sqlserver2016 -Database db1, db2
 
   Will find exact Unused indexes on both db1 and db2 databases
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sqlserver2016
 
   Will find exact Unused indexes on all user databases
 #>

    [CmdletBinding(SupportsShouldProcess = $true)]
    Param (
        [parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [Alias("ServerInstance", "SqlServer")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]
        $SqlCredential,
        [Alias("Databases")]
        [object[]]$Database,
        [object[]]$ExcludeDatabase,
        [Alias("OutFile", "Path")]
        [string]$FilePath,
        [switch]$NoClobber,
        [switch]$Append,
        [switch]$Silent
    )

    begin {

        # Support Compression 2008+
        $unusedQuery = "
  SELECT DB_NAME(database_id) AS 'DatabaseName', s.name AS 'SchemaName', t.name AS 'TableName', i.object_id , i.name AS 'IndexName', i.index_id, i.type_desc , user_seeks , user_scans , user_lookups , user_updates , last_user_seek , last_user_scan , last_user_lookup , last_user_UPDATE , system_seeks , system_scans , system_lookups , system_updates , last_system_seek , last_system_scan , last_system_lookup , last_system_update
  FROM SYS.TABLES T
  JOIN SYS.SCHEMAS S
   ON T.schema_id = s.schema_id
  JOIN SYS.indexes i
   ON i.object_id = t.object_id LEFT OUTER
  JOIN sys.dm_db_index_usage_stats iu
   ON iu.object_id = i.object_id
    AND iu.index_id = i.index_id
  WHERE iu.database_id = DB_ID()
    AND OBJECTPROPERTY(i.[object_id], 'IsMSShipped') = 0
    AND user_seeks = 0
    AND user_scans = 0
    AND user_lookups = 0
    AND i.type_desc NOT IN ('HEAP', 'CLUSTERED COLUMNSTORE')"


        if ($FilePath.Length -gt 0) {
            if ($FilePath -notlike "*\*") { $FilePath = ".\$FilePath" }
            $directory = Split-Path $FilePath
            $exists = Test-Path $directory

            if ($exists -eq $false) {
                Stop-Function -Message "Parent directory $directory does not exist."
                return
            }
        }

        Write-Message -Level Output -Message "Attempting to connect to Sql Server.."
        $server = Connect-SqlInstance -SqlInstance $SqlInstance -SqlCredential $SqlCredential
    }
    process {
        if (Test-FunctionInterrupt) { return }

        if ($server.VersionMajor -lt 9) {
            Stop-Function -Message "This function does not support versions lower than SQL Server 2005 (v9)"
            return
        }

        $lastRestart = $server.Databases['tempdb'].CreateDate
        $endDate = Get-Date -Date $lastRestart
        $diffDays = (New-TimeSpan -Start $endDate -End (Get-Date)).Days

        if ($diffDays -le 6) {
            Stop-Function -Message "The SQL Service was restarted on $lastRestart, which is not long enough for a solid evaluation."
            return
        }

        <#
   Validate if server version is:
    - sql 2012 and if have SP3 CU3 (Build 6537) or higher
    - sql 2014 and if have SP2 (Build 5000) or higher
   If the major version is the same but the build is lower, throws the message
  #>

        if (
            ($server.VersionMajor -eq 11 -and $server.BuildNumber -lt 6537) `
                -or ($server.VersionMajor -eq 12 -and $server.BuildNumber -lt 5000)
        ) {
            Stop-Function -Message "This SQL version has a known issue. Rebuilding an index clears any existing row entry from sys.dm_db_index_usage_stats for that index.`r`nPlease refer to connect item: https://connect.microsoft.com/sqlserver/feedback/details/739566/rebuilding-an-index-clears-stats-from-sys-dm-db-index-usage-stats"
            return
        }

        if ($diffDays -le 33) {
            Write-Message -Level Warning -Message "The SQL Service was restarted on $lastRestart, which may not be long enough for a solid evaluation."
        }

        if ($pipedatabase.Length -gt 0) {
            $database = $pipedatabase.name
        }

        if ($database.Count -eq 0) {
            $database = ($server.Databases | Where-Object { $_.IsSystemObject -eq 0 -and $_.IsAccessible}).Name
        }

        if ($database.Count -gt 0) {
            foreach ($db in $database) {
                if ($ExcludeDatabase -contains $db -or $null -eq $server.Databases[$db]) { continue }
                if ($server.Databases[$db].IsAccessible -eq $false) {
                    Write-Message -Level Warning -Message "Database [$db] is not accessible."
                    continue
                }
                try {
                    Write-Message -Level Output -Message "Getting indexes from database '$db'"

                    $sql = $unusedQuery

                    $unusedIndex = $server.Databases[$db].ExecuteWithResults($sql)

                    $scriptGenerated = $false

                    if ($unusedIndex.Tables[0].Rows.Count -gt 0) {
                        $indexesToDrop = $unusedIndex.Tables[0] | Out-GridView -Title "Unused Indexes on $($db) database - Choose indexes to generate DROP script" -PassThru

                        #When only 1 line selected, the count does not work
                        if ($indexesToDrop.Count -gt 0 -or !([string]::IsNullOrEmpty($indexesToDrop))) {
                            #reset to #Yes
                            $result = 0

                            if ($unusedIndex.Tables[0].Rows.Count -eq $indexesToDrop.Count) {
                                $title = "Indexes to drop on databases '$db':"
                                $message = "You will generate drop statements to all indexes.`r`nPerhaps you want to keep at least one.`r`nDo you wish to generate the script anyway? (Y/N)"
                                $yes = New-Object System.Management.Automation.Host.ChoiceDescription "&Yes", "Will continue"
                                $no = New-Object System.Management.Automation.Host.ChoiceDescription "&No", "Will exit"
                                $options = [System.Management.Automation.Host.ChoiceDescription[]]($yes, $no)
                                $result = $host.ui.PromptForChoice($title, $message, $options, 0)
                            }

                            #default OR answer = YES
                            if ($result -eq 0) {
                                $sqlout = "/*`r`n"
                                $sqlout += "`tScript generated @ $(Get-Date -format "yyyy-MM-dd HH:mm:ss.ms")`r`n"
                                $sqlout += "`tDatabase: $($db)`r`n"
                                $sqlout += "`tConfirm that you have choosen the right indexes before execute the drop script`r`n"
                                $sqlout += "*/`r`n"

                                foreach ($index in $indexesToDrop) {
                                    if ($FilePath.Length -gt 0) {
                                        Write-Message -Level Output -Message "Exporting $($index.TableName).$($index.IndexName)"
                                    }

                                    $sqlout += "USE [$($index.DatabaseName)]`r`n"
                                    $sqlout += "GO`r`n"
                                    $sqlout += "IF EXISTS (SELECT 1 FROM sys.indexes WHERE [object_id] = OBJECT_ID('$($index.SchemaName).$($index.TableName)') AND name = '$($index.IndexName)')`r`n"
                                    $sqlout += " DROP INDEX $($index.SchemaName).$($index.TableName).$($index.IndexName)`r`n"
                                    $sqlout += "GO`r`n`r`n"
                                }

                                if ($FilePath.Length -gt 0) {
                                    $sqlout | Out-File -FilePath $FilePath -Append:$Append -NoClobber:$NoClobber
                                }
                                else {
                                    $sqlout
                                }

                                $scriptGenerated = $true
                            }
                            #answer = no
                            else {
                                Write-Message -Level Warning -Message "Script will not be generated for database '$db'"
                            }
                        }
                    }
                    else {
                        Write-Message -Level Output -Message "No Unused indexes found!"
                    }
                }
                catch {
                    Stop-Function -Message "Issue gathering indexes" -Category InvalidOperation -InnerErrorRecord $_ -Target $db
                }
            }

            if ($scriptGenerated) {
                Write-Message -Level Warning -Message "Confirm the generated script before execute!"
            }
            if ($FilePath.Length -gt 0) {
                Write-Message -Level Output -Message "Script generated to $FilePath"
            }
        }
        else {
            Write-Message -Level Output -Message "There are no databases to analyse."
        }
    }
    end {
        if (Test-FunctionInterrupt) { return }
        Test-DbaDeprecation -DeprecatedOn "1.0.0" -Alias Get-SqlUnusedIndex
    }
}