Communications between NDB cluster nodes are normally handled using TCP/IP. The shared memory (SHM) transporter is distinguished by the fact that signals are transmitted by writing in memory rather than on a socket. The shared-memory transporter (SHM) can improve performance by negating up to 20% of the overhead required by a TCP connection when running an API node (usually an SQL node) and a data node together on the same host. You can enable a shared memory connection in either of the two ways listed here:
By setting the
UseShm
data node configuration parameter to1
, and settingHostName
for the data node andHostName
for the API node to the same value.By using
[shm]
sections in the cluster configuration file, each containing settings forNodeId1
andNodeId2
. This method is described in more detail later in this section.
Suppose a cluster is running a data node which has node ID 1 and an SQL node having node ID 51 on the same host computer at 10.0.0.1. To enable an SHM connection between these two nodes, all that is necessary is to insure that the following entries are included in the cluster configuration file:
[ndbd]
NodeId=1
HostName=10.0.0.1
UseShm=1
[mysqld]
NodeId=51
HostName=10.0.0.1
The two entries just shown are in addition to any other entries and parameter settings needed by the cluster. A more complete example is shown later in this section.
Before starting data nodes that use SHM connections, it is also
necessary to make sure that the operating system on each
computer hosting such a data node has sufficient memory
allocated to shared memory segments. See the documentation for
your operating platform for information regarding this. In
setups where multiple hosts are each running a data node and an
API node, it is possible to enable shared memory on all such
hosts by setting UseShm
in the [ndbd
default]
section of the configuration file. This is
shown in the example later in this section.
While not strictly required, tuning for all SHM connections in
the cluster can be done by setting one or more of the following
parameters in the [shm default]
section of
the cluster configuration (config.ini
)
file:
ShmSize
: Shared memory sizeShmSpinTime
: Time in µs to spin before sleepingSendBufferMemory
: Size of buffer for signals sent from this node, in bytes.SendSignalId
: Indicates that a signal ID is included in each signal sent through the transporter.Checksum
: Indicates that a checksum is included in each signal sent through the transporter.PreSendChecksum
: Checks of the checksum are made prior to sending the signal; Checksum must also be enabled for this to work
This example shows a simple setup with SHM connections defined on multiple hosts, in an NDB Cluster using 3 computers listed here by host name, hosting the node types shown:
10.0.0.0
: The management server10.0.0.1
: A data node and an SQL node10.0.0.2
: A data node and an SQL node
In this scenario, each data node communicates with both the management server and the other data node using TCP transporters; each SQL node uses a shared memory transporter to communicate with the data nodes that is local to it, and a TCP transporter to communicate with the remote data node. A basic configuration reflecting this setup is enabled by the config.ini file whose contents are shown here:
[ndbd default]
DataDir=/path/to/datadir
UseShm=1
[shm default]
ShmSize=8M
ShmSpintime=200
SendBufferMemory=4M
[tcp default]
SendBufferMemory=8M
[ndb_mgmd]
NodeId=49
Hostname=10.0.0.0
DataDir=/path/to/datadir
[ndbd]
NodeId=1
Hostname=10.0.0.1
DataDir=/path/to/datadir
[ndbd]
NodeId=2
Hostname=10.0.0.2
DataDir=/path/to/datadir
[mysqld]
NodeId=51
Hostname=10.0.0.1
[mysqld]
NodeId=52
Hostname=10.0.0.2
[api]
[api]
Parameters affecting all shared memory transporters are set in
the [shm default]
section; these can be
overridden on a per-connection basis in one or more
[shm]
sections. Each such section must be
associated with a given SHM connection using
NodeId1
and
NodeId2
; the values
required for these parameters are the node IDs of the two nodes
connected by the transporter. You can also identify the nodes by
host name using HostName1
and HostName2
, but these
parameters are not required.
The API nodes for which no host names are set use the TCP
transporter to communicate with data nodes independent of the
hosts on which they are started; the parameters and values set
in the [tcp default]
section of the
configuration file apply to all TCP transporters in the cluster.
For optimum performance, you can define a spin time for the SHM
transporter (ShmSpinTime
parameter); this affects both the data node receiver thread and
the poll owner (receive thread or user thread) in
NDB
.
-
Version (or later) NDB 8.0.13 Type or units boolean Default true Range true, false Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
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.
-
Version (or later) NDB 8.0.13 Type or units unsigned Default 35 Range 0 - 200 Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
Determines the group proximity; a smaller value is interpreted as being closer. The default value is sufficient for most conditions.
-
Version (or later) NDB 8.0.13 Type or units name or IP address Default [...] Range ... Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
The
HostName1
andHostName2
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. -
Version (or later) NDB 8.0.13 Type or units name or IP address Default [...] Range ... Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
The
HostName1
andHostName2
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. -
Version (or later) NDB 8.0.13 Type or units numeric Default [none] Range 1 - 255 Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
To identify a connection between two nodes it is necessary to provide node identifiers for each of them, as
NodeId1
andNodeId2
. -
Version (or later) NDB 8.0.13 Type or units numeric Default [none] Range 1 - 255 Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
To identify a connection between two nodes it is necessary to provide node identifiers for each of them, as
NodeId1
andNodeId2
. -
Version (or later) NDB 8.0.13 Type or units numeric Default [none] Range 1 - 63 Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
Identify the server end of a shared memory connection. By default, this is the node ID of the data node.
-
Version (or later) NDB 8.0.13 Type or units bytes Default 0 Range 0 - 4294967039 (0xFFFFFEFF) Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
When more than this many unsent bytes are in the send buffer, the connection is considered overloaded. See Section 25.4.3.14, “Configuring NDB Cluster Send Buffer Parameters”, and Section 25.6.16.65, “The ndbinfo transporters Table”, for more information.
-
Version (or later) NDB 8.0.13 Type or units boolean Default false Range true, false Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
If this parameter and
Checksum
are both enabled, perform pre-send checksum checks, and check all SHM signals between nodes for errors. Has no effect ifChecksum
is not also enabled. -
Version (or later) NDB 8.0.13 Type or units integer Default 2M Range 256K - 4294967039 (0xFFFFFEFF) Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
Size (in bytes) of the shared memory buffer for signals sent from this node using a shared memory connection.
-
Version (or later) NDB 8.0.13 Type or units boolean Default false Range true, false Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
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. -
Version (or later) NDB 8.0.13 Type or units unsigned Default 0 Range 0 - 4294967039 (0xFFFFFEFF) Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
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. If
UseShm
is enabled, the shared memory key is calculated automatically byNDB
. -
Version (or later) NDB 8.0.13 Type or units bytes Default 4M Range 64K - 4294967039 (0xFFFFFEFF) Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
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 4MB. -
Version (or later) NDB 8.0.13 Type or units integer Default 0 Range 0 - 2000 Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
When receiving, the time to wait before sleeping, in microseconds.
-
Version (or later) NDB 8.0.13 Type or units unsigned Default [...] Range 0 - 4294967039 (0xFFFFFEFF) Deprecated Yes (in NDB 7.6) Restart Type Node Restart: Requires a rolling restart of the cluster. (NDB 8.0.13)
This parameter was used formerly to override operating system signal numbers; in NDB 8.0, it is no longer used, and any setting for it is ignored.
Restart types. Information about the restart types used by the parameter descriptions in this section is shown in the following table:
Table 25.22 NDB Cluster restart types
Symbol | Restart Type | Description |
---|---|---|
N | Node | The parameter can be updated using a rolling restart (see Section 25.6.5, “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 |