functions/Test-DbaIdentityUsage.ps1

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function Test-DbaIdentityUsage {
    <#
    .SYNOPSIS
        Displays information relating to IDENTITY seed usage. Works on SQL Server 2008 and above.
 
    .DESCRIPTION
        IDENTITY seeds have max values based off of their data type. This module will locate identity columns and report the seed usage.
 
    .PARAMETER SqlInstance
        Allows you to specify a comma separated list of servers to query.
 
    .PARAMETER SqlCredential
        Allows you to login to servers using SQL Logins as opposed to Windows Auth/Integrated/Trusted. To use:
        $cred = Get-Credential, this pass this $cred to the param.
 
        Windows Authentication will be used if DestinationSqlCredential is not specified. 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 Threshold
        Allows you to specify a minimum % of the seed range being utilized. This can be used to ignore seeds that have only utilized a small fraction of the range.
 
    .PARAMETER NoSystemDb
        Allows you to suppress output on system databases
 
    .PARAMETER Silent
        Use this switch to disable any kind of verbose messages
 
    .NOTES
        Author: Brandon Abshire, netnerds.net
        Tags: Identity
 
        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/Test-DbaIdentityUsage
 
    .EXAMPLE
        Test-DbaIdentityUsage -SqlInstance sql2008, sqlserver2012
        Check identity seeds for servers sql2008 and sqlserver2012.
 
    .EXAMPLE
        Test-DbaIdentityUsage -SqlInstance sql2008 -Database TestDB
        Check identity seeds on server sql2008 for only the TestDB database
 
    .EXAMPLE
        Test-DbaIdentityUsage -SqlInstance sql2008 -Database TestDB -Threshold 20
        Check identity seeds on server sql2008 for only the TestDB database, limiting results to 20% utilization of seed range or higher
    #>

    [CmdletBinding()]
    Param (
        [parameter(Position = 0, Mandatory = $true, ValueFromPipeline = $True)]
        [Alias("ServerInstance", "SqlServer", "SqlServers")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]
        $SqlCredential,
        [Alias("Databases")]
        [object[]]$Database,
        [object[]]$ExcludeDatabase,
        [parameter(Position = 1, Mandatory = $false)]
        [int]$Threshold = 0,
        [parameter(Position = 2, Mandatory = $false)]
        [switch]$NoSystemDb,
        [switch]$Silent
    )

    BEGIN {
        
        $sql = ";WITH CTE_1
        AS
        (
          SELECT SCHEMA_NAME(o.schema_id) AS SchemaName,
                 OBJECT_NAME(a.Object_id) as TableName,
                 a.Name as ColumnName,
                 seed_value AS SeedValue,
                 CONVERT(bigint, increment_value) as IncrementValue,
 
                 CONVERT(bigint, ISNULL(a.last_value, seed_value)) AS LastValue,
 
                 CONVERT(bigint,
                                (
                                    CONVERT(bigint, ISNULL(last_value, seed_value))
                                    - CONVERT(bigint, seed_value)
                                    + (CASE WHEN CONVERT(bigint, seed_value) <> 0 THEN 1 ELSE 0 END)
                                )
                                /
                                CONVERT(bigint, increment_value)
                        ) AS NumberOfUses,
 
                 -- Divide by increment_value to shows the max number of values that can be used
                 -- E.g: smallint identity column that starts on the lower possible value (-32768) and have an increment of 2 will only accept ABS(32768 - 32767 - 1) / 2 = 32768 rows
                 CAST(
                        --ABS(
                        CONVERT(bigint, seed_value)
                        -
                        Case
                            When b.name = 'tinyint' Then 255
                            When b.name = 'smallint' Then 32767
                            When b.name = 'int' Then 2147483647
                            When b.name = 'bigint' Then 9223372036854775807
                        End
                        -
                        -- When less than 0 the 0 counts too
                        CASE
                            WHEN CONVERT(bigint, seed_value) <= 0 THEN 1
                            ELSE 0
                            END
                        --)
                        / CONVERT(bigint, increment_value)
                    AS Numeric(20, 0)) AS MaxNumberRows
            FROM sys.identity_columns a
                INNER JOIN sys.objects o
                   ON a.object_id = o.object_id
                INNER JOIN sys.types As b
                   ON a.system_type_id = b.system_type_id
          WHERE a.seed_value is not null
        ),
        CTE_2
        AS
        (
        SELECT SchemaName, TableName, ColumnName, CONVERT(BIGINT, SeedValue) AS SeedValue, CONVERT(BIGINT, IncrementValue) AS IncrementValue, LastValue, ABS(CONVERT(FLOAT,MaxNumberRows)) AS MaxNumberRows, NumberOfUses,
               CONVERT(Numeric(18,2), ((CONVERT(Float, NumberOfUses) / ABS(CONVERT(FLOAT,MaxNumberRows)) * 100))) AS [PercentUsed]
          FROM CTE_1
        )
        SELECT DB_NAME() as DatabaseName, SchemaName, TableName, ColumnName, SeedValue, IncrementValue, LastValue, MaxNumberRows, NumberOfUses, [PercentUsed]
          FROM CTE_2"


        if ($Threshold -gt 0) { 
            $sql += " WHERE [PercentUsed] >= " + $Threshold + " ORDER BY [PercentUsed] DESC" 
        }
        else { 
            $sql += " ORDER BY [PercentUsed] DESC" 
        }
    }

    process {
        foreach ($instance in $SqlInstance) {
            Write-Message -Level Verbose -Message "Attempting to connect to $instance"
            
            try {
                $server = Connect-SqlInstance -SqlInstance $instance -SqlCredential $SqlCredential
            }
            catch {
                Stop-Function -Message "Failure" -Category ConnectionError -ErrorRecord $_ -Target $instance -Continue
            }
            
            if ($server.versionMajor -lt 10) {
                Stop-Function -Message "This function does not support versions lower than SQL Server 2008 (v10). Skipping server $instance." -Continue
            }            
            
            $dbs = $server.Databases
            
            if ($Database) {
                $dbs = $dbs | Where-Object {$Database -contains $_.Name}
            }
            
            if ($ExcludeDatabase) {
                $dbs = $dbs | Where-Object Name -NotIn $ExcludeDatabase
            }
            
            if ($NoSystemDb) {
                $dbs = $dbs | Where-Object IsSystemObject -eq $false
            }
            
            foreach ($db in $dbs) {
                Write-Message -Level Verbose -Message "Processing $db on $instance"
                
                if ($db.IsAccessible -eq $false) {
                    Stop-Function -Message "The database $db is not accessible. Skipping database." -Continue
                }
                
                foreach ($row in $db.ExecuteWithResults($sql).Tables[0]) {
                    if ($row.PercentUsed -eq [System.DBNull]::Value) {
                        continue
                    }
                    
                    if ($row.PercentUsed -ge $threshold) {
                        [PSCustomObject]@{
                            ComputerName   = $server.NetName
                            InstanceName   = $server.ServiceName
                            SqlInstance    = $server.DomainInstanceName
                            Database       = $row.DatabaseName
                            Schema         = $row.SchemaName
                            Table          = $row.TableName
                            Column         = $row.ColumnName
                            SeedValue      = $row.SeedValue
                            IncrementValue = $row.IncrementValue
                            LastValue      = $row.LastValue
                            MaxNumberRows  = $row.MaxNumberRows
                            NumberOfUses   = $row.NumberOfUses
                            PercentUsed    = $row.PercentUsed
                        }
                    }
                }
            }
        }
    }
}