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 clicking OK the drop statement will be generated.
 
        .PARAMETER SqlInstance
   The SQL Server you want to check for unused indexes.
         
        .PARAMETER SqlCredential
    Allows you to login to servers using SQL Logins instead of Windows Authentication (AKA Integrated or Trusted). To use:
 
   $cred = Get-Credential, then pass $cred 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. Options for this list are auto-populated from the server. If unspecified, all databases will be processed.
 
  .PARAMETER ExcludeDatabase
   Specifies the database(s) to exclude from processing. Options for this list are auto-populated from the server.
 
  .PARAMETER FilePath
   Specifies the path of a file to write the DROP statements to.
 
  .PARAMETER NoClobber
   If this switch is enabled, the output file will not be overwritten.
    
  .PARAMETER Append
   If this switch is enabled, content will be appended to the output file.
 
  .PARAMETER IgnoreUptime
   Less than 7 days uptime can mean that analysis of unused indexes is unreliable, and normally no results will be returned. By setting this option results will be returned even if the Instance has been running for less that 7 days.        
 
   .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: Indexes
   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
 
   Generates the SQL statements to drop the selected unused indexes on server "sql2005". The statements are written to the file "C:\temp\sql2005-UnusedIndexes.sql"
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sql2005 -FilePath C:\temp\sql2005-UnusedIndexes.sql -Append
 
   Generates the SQL statements to drop the selected unused indexes on server "sql2005". The statements are written to the file "C:\temp\sql2005-UnusedIndexes.sql", appending if the file already exists.
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sqlserver2016 -SqlCredential $cred
 
   Generates the SQL statements to drop the selected unused indexes on server "sqlserver2016", using SQL Authentication to connect to the database.
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sqlserver2016 -Database db1, db2
 
   Generates the SQL Statement to to drop selected indexes in databases db1 & db2 on server "sqlserver2016".
 
  .EXAMPLE
   Find-DbaUnusedIndex -SqlInstance sqlserver2016
 
   Generates the SQL statements to drop selected indexes on all user databases.
 
  .EXAMPLE
   Fine-DbaUnusedIndex -SqlInstance sqlserver2016 -IgnoreUptime
    
   Generates the SQL statements to drop selected indexes on all user databases even if the instance has been online for less than 7 days.
   Note that results may not have enough detail for all indexes, so care should be taken when using them or the generated scripts. Best practice is to allow a full week to capture the mmajority of index use cases
 
 #>

    [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]$IgnoreUptime,
        [switch][Alias('Silent')]$EnableException
    )

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

        <#
   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 chosen 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
    }
}