SQL Server的MAXDOP设置算法

Question

在设置新Server时，我使用以下代码确定MAXDOP设置的良好起点：

/* 
   This will recommend a MAXDOP setting appropriate for your machine's NUMA memory
   configuration.  You will need to evaluate this setting in a non-production 
   environment before moving it to production.

   MAXDOP can be configured using:  
   EXEC sp_configure 'max degree of parallelism',X;
   RECONFIGURE

   If this instance is hosting a Sharepoint database, you MUST specify MAXDOP=1 
   (URL wrapped for readability)
   http://blogs.msdn.com/b/rcormier/archive/2012/10/25/
   you-shall-configure-your-maxdop-when-using-sharepoint-2013.aspx

   Biztalk (all versions, including 2010): 
   MAXDOP = 1 is only required on the BizTalk Message Box
   database server(s), and must not be changed; all other servers hosting other 
   BizTalk Server databases may return this value to 0 if set.
   http://support.microsoft.com/kb/899000
*/


DECLARE @CoreCount int;
DECLARE @NumaNodes int;

SET @CoreCount = (SELECT i.cpu_count from sys.dm_os_sys_info i);
SET @NumaNodes = (
    SELECT MAX(c.memory_node_id) + 1 
    FROM sys.dm_os_memory_clerks c 
    WHERE memory_node_id < 64
    );

IF @CoreCount > 4 /* If less than 5 cores, don't bother. */
BEGIN
    DECLARE @MaxDOP int;

    /* 3/4 of Total Cores in Machine */
    SET @MaxDOP = @CoreCount * 0.75; 

    /* if @MaxDOP is greater than the per NUMA node
       Core Count, set @MaxDOP = per NUMA node core count
    */
    IF @MaxDOP > (@CoreCount / @NumaNodes) 
        SET @MaxDOP = (@CoreCount / @NumaNodes) * 0.75;

    /*
        Reduce @MaxDOP to an even number 
    */
    SET @MaxDOP = @MaxDOP - (@MaxDOP % 2);

    /* Cap MAXDOP at 8, according to Microsoft */
    IF @MaxDOP > 8 SET @MaxDOP = 8;

    PRINT 'Suggested MAXDOP = ' + CAST(@MaxDOP as varchar(max));
END
ELSE
BEGIN
    PRINT 'Suggested MAXDOP = 0 since you have less than 4 cores total.';
    PRINT 'This is the default setting, you likely do not need to do';
    PRINT 'anything.';
END

我意识到这有点主观，而且可能会根据许多事情而有所不同；然而，我正在尝试创建一个完整的代码来作为新服务器的起点。

有人对这段代码有任何输入吗？

Answer 1

最好的方法是--使用coreinfo (sysinternals的实用程序)，因为这将给您提供

a. Logical to Physical Processor Map
b. Logical Processor to Socket Map
c. Logical Processor to NUMA Node Map as below :

Logical to Physical Processor Map:
**----------------------  Physical Processor 0 (Hyperthreaded)
--**--------------------  Physical Processor 1 (Hyperthreaded)
----**------------------  Physical Processor 2 (Hyperthreaded)
------**----------------  Physical Processor 3 (Hyperthreaded)
--------**--------------  Physical Processor 4 (Hyperthreaded)
----------**------------  Physical Processor 5 (Hyperthreaded)
------------**----------  Physical Processor 6 (Hyperthreaded)
--------------**--------  Physical Processor 7 (Hyperthreaded)
----------------**------  Physical Processor 8 (Hyperthreaded)
------------------**----  Physical Processor 9 (Hyperthreaded)
--------------------**--  Physical Processor 10 (Hyperthreaded)
----------------------**  Physical Processor 11 (Hyperthreaded)
 
Logical Processor to Socket Map:
************------------  Socket 0
------------************  Socket 1
 
Logical Processor to NUMA Node Map:
************------------  NUMA Node 0
------------************  NUMA Node 1

现在，基于上述信息，理想的MaxDop设置应该计算为

a.  It has 12 CPU’s which are hyper threaded giving us 24 CPUs.
b.  It has 2 NUMA node [Node 0 and 1] each having 12 CPU’s with Hyperthreading ON.
c.  Number of sockets are 2 [socket 0 and 1] which are housing 12 CPU’s each.

Considering all above factors, the max degree of Parallelism should be set to 6 which is ideal value for server with above configuration.

因此，答案是--“这取决于”您的处理器占用情况，NUMA配置和下表将总结我前面解释的内容：

8 or less processors    ===> 0 to N (where N= no. of processors)
More than 8 processors  ===> 8
NUMA configured         ===> MAXDOP should not exceed no of CPU’s assigned to each 
                                 NUMA node with max value capped to 8
Hyper threading Enabled ===> Should not exceed the number of physical processors.

编辑:下面是一个快速而肮脏的TSQL脚本，用于生成MAXDOP设置的建议

/*************************************************************************
Author          :   Kin Shah
Purpose         :   Recommend MaxDop settings for the server instance
Tested RDBMS    :   SQL Server 2008R2

**************************************************************************/
declare @hyperthreadingRatio bit
declare @logicalCPUs int
declare @HTEnabled int
declare @physicalCPU int
declare @SOCKET int
declare @logicalCPUPerNuma int
declare @NoOfNUMA int

select @logicalCPUs = cpu_count -- [Logical CPU Count]
    ,@hyperthreadingRatio = hyperthread_ratio --  [Hyperthread Ratio]
    ,@physicalCPU = cpu_count / hyperthread_ratio -- [Physical CPU Count]
    ,@HTEnabled = case 
        when cpu_count > hyperthread_ratio
            then 1
        else 0
        end -- HTEnabled
from sys.dm_os_sys_info
option (recompile);

select @logicalCPUPerNuma = COUNT(parent_node_id) -- [NumberOfLogicalProcessorsPerNuma]
from sys.dm_os_schedulers
where [status] = 'VISIBLE ONLINE'
    and parent_node_id < 64
group by parent_node_id
option (recompile);

select @NoOfNUMA = count(distinct parent_node_id)
from sys.dm_os_schedulers -- find NO OF NUMA Nodes 
where [status] = 'VISIBLE ONLINE'
    and parent_node_id < 64

-- Report the recommendations ....
select
    --- 8 or less processors and NO HT enabled
    case 
        when @logicalCPUs < 8
            and @HTEnabled = 0
            then 'MAXDOP setting should be : ' + CAST(@logicalCPUs as varchar(3))
                --- 8 or more processors and NO HT enabled
        when @logicalCPUs >= 8
            and @HTEnabled = 0
            then 'MAXDOP setting should be : 8'
                --- 8 or more processors and HT enabled and NO NUMA
        when @logicalCPUs >= 8
            and @HTEnabled = 1
            and @NoofNUMA = 1
            then 'MaxDop setting should be : ' + CAST(@logicalCPUPerNuma / @physicalCPU as varchar(3))
                --- 8 or more processors and HT enabled and NUMA
        when @logicalCPUs >= 8
            and @HTEnabled = 1
            and @NoofNUMA > 1
            then 'MaxDop setting should be : ' + CAST(@logicalCPUPerNuma / @physicalCPU as varchar(3))
        else ''
        end as Recommendations

编辑:对于未来的访问者，您可以查看测试-dbamaxdop powershell函数(以及其他非常有用的DBA函数 (都是免费的！)。

Answer 2

在设置MAXDOP时，通常希望将其限制为NUMA节点中的核数。这样，调度就不会试图跨numa节点访问内存。

Answer 3

看看来自MSDN团队的帖子，我想出了一种方法来可靠地从机器中获取物理核心计数，并使用它来确定一个好的MAXDOP设置。

所谓“好”，我指的是保守。也就是说，我的要求是在NUMA节点中最多使用75%的核心，或者使用最多8个核心。

Server 2016 (13.x) SP2及以上版本，以及Server 2017及以上所有版本的有关每个套接字物理核心计数、套接字计数和NUMA节点数目的表面详细信息，从而为确定新Server安装的基准MAXDOP设置提供了一种整洁的方法。

对于上面提到的版本，此代码将建议保守的MAXDOP设置为NUMA节点中物理核数量的75%：

DECLARE @socket_count int;
DECLARE @cores_per_socket int;
DECLARE @numa_node_count int;
DECLARE @memory_model nvarchar(120);
DECLARE @hyperthread_ratio int;

SELECT @socket_count = dosi.socket_count
       , @cores_per_socket = dosi.cores_per_socket
       , @numa_node_count = dosi.numa_node_count
       , @memory_model = dosi.sql_memory_model_desc
       , @hyperthread_ratio = dosi.hyperthread_ratio
FROM sys.dm_os_sys_info dosi;

SELECT [Socket Count] = @socket_count
       , [Cores Per Socket] = @cores_per_socket
       , [Number of NUMA nodes] = @numa_node_count
       , [Hyperthreading Enabled] = CASE WHEN @hyperthread_ratio > @cores_per_socket THEN 1 ELSE 0 END
       , [Lock Pages in Memory granted?] = CASE WHEN @memory_model = N'CONVENTIONAL' THEN 0 ELSE 1 END;

DECLARE @MAXDOP int = @cores_per_socket;
SET @MAXDOP = @MAXDOP * 0.75;
IF @MAXDOP >= 8 SET @MAXDOP = 8;

SELECT [Recommended MAXDOP setting] = @MAXDOP
       , [Command] = 'EXEC sys.sp_configure N''max degree of parallelism'', ' + CONVERT(nvarchar(10), @MAXDOP) + ';RECONFIGURE;';

对于Server 2017或Server 2016 SP2之前的Server版本，您无法从sys.dm_os_sys_info获取每个numa节点的核心计数。相反，我们可以使用PowerShell来确定物理核心计数：

powershell -OutputFormat Text -NoLogo -Command "& {Get-WmiObject -namespace 
"root\CIMV2" -class Win32_Processor -Property NumberOfCores} | select NumberOfCores"

还可以使用PowerShell来确定逻辑核的数量，如果打开HyperThreading，逻辑核的数量很可能是物理核的两倍：

powershell -OutputFormat Text -NoLogo -Command "& {Get-WmiObject -namespace 
"root\CIMV2" -class Win32_Processor -Property NumberOfCores} 
| select NumberOfLogicalProcessors"

：

/* 
   This will recommend a MAXDOP setting appropriate for your machine's NUMA memory
   configuration.  You will need to evaluate this setting in a non-production 
   environment before moving it to production.

   MAXDOP can be configured using:  
   EXEC sp_configure 'max degree of parallelism',X;
   RECONFIGURE

   If this instance is hosting a Sharepoint database, you MUST specify MAXDOP=1 
   (URL wrapped for readability)
   http://blogs.msdn.com/b/rcormier/archive/2012/10/25/
   you-shall-configure-your-maxdop-when-using-sharepoint-2013.aspx

   Biztalk (all versions, including 2010): 
   MAXDOP = 1 is only required on the BizTalk Message Box
   database server(s), and must not be changed; all other servers hosting other 
   BizTalk Server databases may return this value to 0 if set.
   http://support.microsoft.com/kb/899000
*/
SET NOCOUNT ON;

DECLARE @CoreCount int;
SET @CoreCount = 0;
DECLARE @NumaNodes int;

/*  see if xp_cmdshell is enabled, so we can try to use 
    PowerShell to determine the real core count
*/
DECLARE @T TABLE (
    name varchar(255)
    , minimum int
    , maximum int
    , config_value int
    , run_value int
);
INSERT INTO @T 
EXEC sp_configure 'xp_cmdshell';
DECLARE @cmdshellEnabled BIT;
SET @cmdshellEnabled = 0;
SELECT @cmdshellEnabled = 1 
FROM @T
WHERE run_value = 1;
IF @cmdshellEnabled = 1
BEGIN
    CREATE TABLE #cmdshell
    (
        txt VARCHAR(255)
    );
    INSERT INTO #cmdshell (txt)
    EXEC xp_cmdshell 'powershell -OutputFormat Text -NoLogo -Command "& {Get-WmiObject -namespace "root\CIMV2" -class Win32_Processor -Property NumberOfCores} | select NumberOfCores"';
    SELECT @CoreCount = CONVERT(INT, LTRIM(RTRIM(txt)))
    FROM #cmdshell
    WHERE ISNUMERIC(LTRIM(RTRIM(txt)))=1;
    DROP TABLE #cmdshell;
END
IF @CoreCount = 0 
BEGIN
    /* 
        Could not use PowerShell to get the corecount, use SQL Server's 
        unreliable number.  For machines with hyperthreading enabled
        this number is (typically) twice the physical core count.
    */
    SET @CoreCount = (SELECT i.cpu_count from sys.dm_os_sys_info i); 
END

SET @NumaNodes = (
    SELECT MAX(c.memory_node_id) + 1 
    FROM sys.dm_os_memory_clerks c 
    WHERE memory_node_id < 64
    );

DECLARE @MaxDOP int;

/* 3/4 of Total Cores in Machine */
SET @MaxDOP = @CoreCount * 0.75; 

/* if @MaxDOP is greater than the per NUMA node
    Core Count, set @MaxDOP = per NUMA node core count
*/
IF @MaxDOP > (@CoreCount / @NumaNodes) 
    SET @MaxDOP = (@CoreCount / @NumaNodes) * 0.75;

/*
    Reduce @MaxDOP to an even number 
*/
SET @MaxDOP = @MaxDOP - (@MaxDOP % 2);

/* Cap MAXDOP at 8, according to Microsoft */
IF @MaxDOP > 8 SET @MaxDOP = 8;

PRINT 'Suggested MAXDOP = ' + CAST(@MaxDOP as varchar(max));