为什么我的 Azure SQL 数据库索引仍然碎片化？

Question

我的公司犯了在我们的 Azure SQL 数据库表上使用 GUID 作为主键的罪行（实际上比这更糟糕：我们使用 VARCHAR(36) 而不是 UNIQUEIDENTIFIER）。因此，我们最终得到了碎片索引。他们看起来像这样：

CREATE TABLE OldTable (
  Id VARCHAR(36) PRIMARY KEY CLUSTERED NOT NULL DEFAULT NEWID(),
  CreateTime DATETIME2 NOT NULL,
  ...
)

我通过创建新表“修复”了这个问题。这一次，我为 CLUSTERED INDEX 使用了一个不可变的、不断增加的 DATETIME2（例如 CreateTime）列，并将 VARCHAR(36) 保留为 PRIMARY KEY，但这次是非集群的。像这样：

CREATE TABLE NewTable (
  Id VARCHAR(36) PRIMARY KEY NONCLUSTERED NOT NULL DEFAULT NEWID(),
  CreateTime DATETIME2 NOT NULL INDEX IX_NewTable_CreateTime CLUSTERED,
)

然后我使用 INSERT INTO NewTable SELECT * FROM OldTable 将旧表中的行“复制”到新表。最后，我重命名了表并删除了旧表。生活似乎很美好。

令我惊讶的是，几周后，我发现 NewTable 有很多碎片索引，平均碎片率高达 80%！甚至 IX_NewTable_CreateTime 也报告了 18% 的碎片。

INSERT INTO 是否使索引碎片化？ REBUILD 索引会永久解决问题吗？

Answer 1

分段将取决于索引字段上的插入/更新频率和索引页面的大小。

出于维护目的，您可以使用 Azure 自动化并创建一个循环脚本来检查碎片索引并对其进行优化。

图库中有一本 Runbook 专门用于此目的：

最好的一点是自动化是免费的，只要您不超过每月 500 分钟的运行时间、合理安排执行时间并且您无需付费 :)

我对图库脚本进行了自定义改进，您也可以随意使用：

<#
.SYNOPSIS 
    Indexes tables in a database if they have a high fragmentation

.DESCRIPTION
    This runbook indexes all of the tables in a given database if the fragmentation is
    above a certain percentage. 
    It highlights how to break up calls into smaller chunks, 
    in this case each table in a database, and use checkpoints. 
    This allows the runbook job to resume for the next chunk of work even if the 
    fairshare feature of Azure Automation puts the job back into the queue every 30 minutes

.PARAMETER SqlServer
    Name of the SqlServer

.PARAMETER Database
    Name of the database

.PARAMETER SQLCredentialName
    Name of the Automation PowerShell credential setting from the Automation asset store. 
    This setting stores the username and password for the SQL Azure server

.PARAMETER FragPercentage
    Optional parameter for specifying over what percentage fragmentation to index database
    Default is 20 percent

 .PARAMETER RebuildOffline
    Optional parameter to rebuild indexes offline if online fails 
    Default is false

 .PARAMETER Table
    Optional parameter for specifying a specific table to index
    Default is all tables

.PARAMETER SqlServerPort
    Optional parameter for specifying the SQL port 
    Default is 1433

.EXAMPLE
    Update-SQLIndexRunbook -SqlServer "server.database.windows.net" -Database "Finance" -SQLCredentialName "FinanceCredentials"

.EXAMPLE
    Update-SQLIndexRunbook -SqlServer "server.database.windows.net" -Database "Finance" -SQLCredentialName "FinanceCredentials" -FragPercentage 30

.EXAMPLE
    Update-SQLIndexRunbook -SqlServer "server.database.windows.net" -Database "Finance" -SQLCredentialName "FinanceCredentials" -Table "Customers" -RebuildOffline $True

.NOTES
    AUTHOR: Matias Quaranta
    LASTEDIT: Jan 10th, 2015 
#>
workflow MyRunBook
{
    param(
        [parameter(Mandatory=$True)]
        [string] $SqlServer,

        [parameter(Mandatory=$True)]
        [string] $Database,

        [parameter(Mandatory=$True)]
        [string] $SQLCredentialName,

        [parameter(Mandatory=$False)]
        [int] $FragPercentage = 20,

        [parameter(Mandatory=$False)]
        [int] $SqlServerPort = 1433,

        [parameter(Mandatory=$False)]
        [boolean] $RebuildOffline = $False,

        [parameter(Mandatory=$False)]
        [string] $Table

    )

    # Get the stored username and password from the Automation credential
    $SqlCredential = Get-AutomationPSCredential -Name $SQLCredentialName
    if ($SqlCredential -eq $null)
    {
        throw "Could not retrieve '$SQLCredentialName' credential asset. Check that you created this first in the Automation service."
    }

    $SqlUsername = $SqlCredential.UserName 
    $SqlPass = $SqlCredential.GetNetworkCredential().Password

    InlineScript{

        # Define the connection to the SQL Database
        $Conn = New-Object System.Data.SqlClient.SqlConnection("Server=tcp:$using:SqlServer,$using:SqlServerPort;Database=$using:Database;User ID=$using:SqlUsername;Password=$using:SqlPass;Trusted_Connection=False;Encrypt=True;Connection Timeout=30;")

        # Open the SQL connection
        $Conn.Open()

        # SQL command to find tables and their average fragmentation
        $SQLCommandString = @"
        SELECT a.object_id, b.name, (select name from sys.tables t where t.object_id = b.object_id) as tablename, avg_fragmentation_in_percent
        FROM sys.dm_db_index_physical_stats (
               DB_ID(N'$Database')
             , OBJECT_ID(0)
             , NULL
             , NULL
             , NULL) AS a
        JOIN sys.indexes AS b 
        ON a.object_id = b.object_id AND a.index_id = b.index_id;
"@
        # Return the tables with their corresponding average fragmentation
        $Cmd=new-object system.Data.SqlClient.SqlCommand($SQLCommandString, $Conn)
        $Cmd.CommandTimeout=120

        # Execute the SQL command
        $FragmentedTable=New-Object system.Data.DataSet
        $Da=New-Object system.Data.SqlClient.SqlDataAdapter($Cmd)
        [void]$Da.fill($FragmentedTable)

 # Return the table names that have high fragmentation
        ForEach ($FragTable in $FragmentedTable.Tables[0])
        {

            If ($FragTable.avg_fragmentation_in_percent -ge $Using:FragPercentage)
            {
                Write-Verbose ("Index found : " +  $FragTable.name + " on table:" + $FragTable.tablename)

                $SQLCommandString = "EXEC('ALTER INDEX "+$FragTable.name+" ON "+$FragTable.tablename+" REBUILD')"

                $Cmd2=new-object system.Data.SqlClient.SqlCommand($SQLCommandString, $Conn)
                # Set the Timeout to be less than 30 minutes since the job will get queued if > 30
                # Setting to 25 minutes to be safe.
                $Cmd2.CommandTimeout=1500

                Try 
                {
                    $Ds=New-Object system.Data.DataSet
                    $Da=New-Object system.Data.SqlClient.SqlDataAdapter($Cmd2)
                    [void]$Da.fill($Ds)
                }
                Catch
                {
                    Write-Verbose ($FragTable.name +" on table "+$FragTable.tablename+" could NOT be indexed.")
                }
            }
        }

        $Conn.Close()
    }
    Write-Verbose "Finished Indexing"
}