18.3.3.11 NDB Cluster Shared-Memory Connections

NDB Cluster attempts to use the shared memory transporter and configure it automatically where possible. [shm] sections in the config.ini file explicitly define shared-memory connections between nodes in the cluster. When explicitly defining shared memory as the connection method, it is necessary to define at least NodeId1, NodeId2, and ShmKey. All other parameters have default values that should work well in most cases.

Important

SHM functionality is considered experimental only. It is not officially supported in any current NDB Cluster release, and testing results indicate that SHM performance is not appreciably greater than when using TCP/IP for the transporter.

For these reasons, you must determine for yourself or by using our free resources (forums, mailing lists) whether SHM can be made to work correctly in your specific case.

• Checksum

  Version (or later)	NDB 7.3.1
  Type or units	boolean
  Default	true
  Range	true, false
  Restart Type	N (NDB 7.3.1)

  This parameter is a boolean (Y/N) parameter which is disabled by default. When it is enabled, checksums for all messages are calculated before being placed in the send buffer.

  This feature prevents messages from being corrupted while waiting in the send buffer. It also serves as a check against data being corrupted during transport.

• Group

  Version (or later)	NDB 7.3.1
  Type or units	unsigned
  Default	35
  Range	0 - 200
  Restart Type	N (NDB 7.3.1)

  Determines the group proximity; a smaller value is interpreted as being closer. The default value is sufficient for most conditions.

• HostName1

  Version (or later)	NDB 7.3.1
  Type or units	name or IP address
  Default	[...]
  Range	...
  Restart Type	N (NDB 7.3.1)

  The HostName1 and HostName2 parameters can be used to specify specific network interfaces to be used for a given SHM connection between two nodes. The values used for these parameters can be host names or IP addresses.

• HostName2

  Version (or later)	NDB 7.3.1
  Type or units	name or IP address
  Default	[...]
  Range	...
  Restart Type	N (NDB 7.3.1)

  The HostName1 and HostName2 parameters can be used to specify specific network interfaces to be used for a given SHM connection between two nodes. The values used for these parameters can be host names or IP addresses.

• NodeId1

  Version (or later)	NDB 7.3.1
  Type or units	numeric
  Default	[none]
  Range	1 - 255
  Restart Type	N (NDB 7.3.1)

  To identify a connection between two nodes it is necessary to provide node identifiers for each of them, as NodeId1 and NodeId2.

• NodeId2

  Version (or later)	NDB 7.3.1
  Type or units	numeric
  Default	[none]
  Range	1 - 255
  Restart Type	N (NDB 7.3.1)

  To identify a connection between two nodes it is necessary to provide node identifiers for each of them, as NodeId1 and NodeId2.

• NodeIdServer

  Version (or later)	NDB 7.3.1
  Type or units	numeric
  Default	[none]
  Range	1 - 63
  Restart Type	N (NDB 7.3.1)

  Identify the server end of a shared memory connection.

• OverloadLimit

  Version (or later)	NDB 7.3.1
  Type or units	bytes
  Default	0
  Range	0 - 4294967039 (0xFFFFFEFF)
  Restart Type	N (NDB 7.3.1)

  When more than this many unsent bytes are in the send buffer, the connection is considered overloaded.

  This parameter can be used to determine the amount of unsent data that must be present in the send buffer before the connection is considered overloaded. See Section 18.3.3.12, “Configuring NDB Cluster Send Buffer Parameters”, for more information.

• SendSignalId

  Version (or later)	NDB 7.3.1
  Type or units	boolean
  Default	false
  Range	true, false
  Restart Type	N (NDB 7.3.1)

  To retrace the path of a distributed message, it is necessary to provide each message with a unique identifier. Setting this parameter to Y causes these message IDs to be transported over the network as well. This feature is disabled by default in production builds, and enabled in -debug builds.

• ShmKey

  Version (or later)	NDB 7.3.1
  Type or units	unsigned
  Default	0
  Range	0 - 4294967039 (0xFFFFFEFF)
  Restart Type	N (NDB 7.3.1)

  When setting up shared memory segments, a node ID, expressed as an integer, is used to identify uniquely the shared memory segment to use for the communication. There is no default value.

• ShmSize

  Version (or later)	NDB 7.3.1
  Type or units	bytes
  Default	1M
  Range	64K - 4294967039 (0xFFFFFEFF)
  Restart Type	N (NDB 7.3.1)

  Each SHM connection has a shared memory segment where messages between nodes are placed by the sender and read by the reader. The size of this segment is defined by ShmSize. The default value is 1MB.

• SigNum

  Version (or later)	NDB 7.3.1
  Type or units	unsigned
  Default	[...]
  Range	0 - 4294967039 (0xFFFFFEFF)
  Deprecated	Yes (in NDB 7.6)
  Restart Type	N (NDB 7.3.1)

  When using the shared memory transporter, a process sends an operating system signal to the other process when there is new data available in the shared memory. Should that signal conflict with an existing signal, this parameter can be used to change it. This is a possibility when using SHM due to the fact that different operating systems use different signal numbers.

  The default value of SigNum is 0; therefore, it must be set to avoid errors in the cluster log when using the shared memory transporter. Typically, this parameter is set to 10 in the [shm default] section of the config.ini file.

Restart types.  Information about the restart types used by the parameter descriptions in this section is shown in the following table:

Table 18.16 NDB Cluster restart types

Symbol	Restart Type	Description
N	Node	The parameter can be updated using a rolling restart (see Section 18.5.5, “Performing a Rolling Restart of an NDB Cluster”)
S	System	All cluster nodes must be shut down completely, then restarted, to effect a change in this parameter
I	Initial	Data nodes must be restarted using the --initial option