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Soft-NUMA (SQL Server)

 

Updated: March 3, 2016

Applies To: SQL Server 2016

Modern processors have multiple to many cores per socket. Each socket is represented, usually, as a single NUMA node. The SQL Server database engine partitions various internal structures and partitions service threads per NUMA node. With processors containing 10 or more cores per socket, using software NUMA to split hardware NUMA nodes generally increases scalability and performance. Prior to SQL Server 2016, software-based NUMA (soft-NUMA) required you to edit the registry to add a node configuration affinity mask and was configured per computer rather than per instance. With SQL Server 2016, soft-NUMA is configured automatically at the database-instance level when the SQL Server service starts.

System_CAPS_noteNote

Hot-add processors are not supported by soft-NUMA.

With SQL Server 2016, whenever the database engine server detects more than 8 logical processors at startup, soft-NUMA nodes are created automatically by default. Physical and hyper-threaded processor cores are not differentiated when counting logical processors. When the number of logical processors detected more than 8 per socket, the database engine service will create soft-NUMA nodes that ideally contain 8 cores, but can go down to 5 or up to 9 logical processors per node. The size of the hardware node can be limited by a CPU affinity mask. See ALTER SERVER CONFIGURATION (Transact-SQL). The number of NUMA nodes will never exceed the maximum number of supported NUMA nodes.

You can disable or re-enable soft-NUMA using the ALTER SERVER CONFIGURATION (Transact-SQL) statement with the SET SOFTNUMA argument. Changing the value of this setting requires a restart of the database engine to take effect.

The figure below shows the type of information regarding soft-NUMA that you will see in the SQL Server error log when SQL Server detects hardware NUMA nodes with greater than 8 logical processors.

Soft-NUMA Error Log

To can manually configure SQL Server to use soft-NUMA by disabling automatic soft_NUMA and editing the registry to add a node configuration affinity mask. When using this method, the soft-NUMA mask can be stated as a binary, DWORD (hexadecimal or decimal), or QWORD (hexadecimal or decimal) registry entry. To configure more than the first 32 CPUs use QWORD or BINARY registry values. (QWORD values cannot be used prior to SQL Server 2012.) After modifying the registry, you must restart the Database Engine for the soft-NUMA configuration to take effect.

System_CAPS_tipTip

CPUs are numbered starting with 0.

Incorrectly editing the registry can severely damage your system. Before making changes to the registry, we recommend that you back up any valued data on the computer.

Consider the following example. A computer with eight CPUs does not have hardware NUMA. Three soft-NUMA nodes are configured. Database Engine instance A is configured to use CPUs 0 through 3. A second instance of the Database Engine is installed and configured to use CPUs 4 through 7. The example can be visually represented as:

CPUs          0  1  2  3  4  5  6  7

Soft-NUMA   <-N0--><-N1-><----N2---->

SQL Server  <instance A ><instance B>

Instance A, which experiences significant I/O, now has two I/O threads and one l azy writer thread, while instance B, which performs processor-intensive operations, has only one I/O thread and one lazy writer thread. Differing amounts of memory can be assigned to the instances, but unlike hardware NUMA, they both receive memory from the same operating system memory block and there is no memory-to-processor affinity.

The lazy writer thread is tied to the SQL OS view of the physical NUMA memory nodes. Therefore, whatever the hardware presents as physical NUMA nodes will equate to the number of lazy writer threads that are created. For more information, see How It Works: Soft NUMA, I/O Completion Thread, Lazy Writer Workers and Memory Nodes.

System_CAPS_noteNote

The Soft-NUMA registry keys are not copied when you upgrade an instance of SQL Server.

Run the following statement on instance A to configure it to use CPUs 0, 1, 2, and 3 by setting the CPU affinity mask:

ALTER SERVER CONFIGURATION 
SET PROCESS AFFINITY CPU=0 TO 3;

Run the following statement on instance B to configure it to use CPUs 4, 5, 6, and 7 by setting the CPU affinity mask:

ALTER SERVER CONFIGURATION 
SET PROCESS AFFINITY CPU=4 TO 7;

Using the Registry Editor program (regedit.exe), add the following registry keys to map soft-NUMA node 0 to CPUs 0 and 1, soft-NUMA node 1 to CPUs 2 and 3, and soft-NUMA node 2 to CPUs 4. 5, 6, and 7.

System_CAPS_tipTip

To specify CPUs 60 through 63, use a QWORD value of F000000000000000 or a BINARY value of 1111000000000000000000000000000000000000000000000000000000000000.

In the following example, assume you have a DL580 G9 server, with 18 cores per socket (in 4 sockets), and each socket is in its own K-group. A soft-numa configuration that you might create would look something like following. (6 cores per Node, 3 nodes per group, 4 groups).

Example for a SQL Server 2016 Release Candidate (RC3) server with multiple K-Groups

Type

Value name

Value data

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node0

DWORD

CPUMask

0x3F

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node0

DWORD

Group

0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node1

DWORD

CPUMask

0x0fc0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node1

DWORD

Group

0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node2

DWORD

CPUMask

0x3f000

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node2

DWORD

Group

0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node3

DWORD

CPUMask

0x3F

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node3

DWORD

Group

1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node4

DWORD

CPUMask

0x0fc0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node4

DWORD

Group

1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node5

DWORD

CPUMask

0x3f000

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node5

DWORD

Group

1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node6

DWORD

CPUMask

0x3F

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node6

DWORD

Group

2

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node7

DWORD

CPUMask

0x0fc0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node7

DWORD

Group

2

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node8

DWORD

CPUMask

0x3f000

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node8

DWORD

Group

2

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node9

DWORD

CPUMask

0x3F

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node9

DWORD

Group

3

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node10

DWORD

CPUMask

0x0fc0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node10

DWORD

Group

3

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node11

DWORD

CPUMask

0x3f000

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\130\NodeConfiguration\Node11

DWORD

Group

3

You can use the following DMVs to view the current state and configuration of soft_NUMA.

System_CAPS_noteNote

While you can view the running value for automatic soft-NUMA using sp_configure (Transact-SQL), you cannot change its value using sp_configure. You must use the ALTER SERVER CONFIGURATION (Transact-SQL) statement with the SET SOFTNUMA argument.

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