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.
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.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | numeric | [none] | ... | N |
To identify a connection between two nodes it is necessary
to provide node identifiers for each of them, as
NodeId1 and
NodeId2.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | numeric | [none] | ... | N |
To identify a connection between two nodes it is necessary
to provide node identifiers for each of them, as
NodeId1 and
NodeId2.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | name or IP address | [none] | ... | N |
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.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | name or IP address | [none] | ... | N |
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.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | bytes | 0 | 0 - 4294967039 (0xFFFFFEFF) | N |
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 18.3.3.13, “Configuring NDB Cluster Send Buffer Parameters”, for more information.
In some older releases, the effective value of this
parameter was limited by the size of
SendBufferMemory; in
NDB Cluster 7.2, the actual value for
OverloadLimit (up to the stated maximum
of 4G) is used instead.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | unsigned | [none] | 0 - 4294967039 (0xFFFFFEFF) | N |
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.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | bytes | 1M | 64K - 4294967039 (0xFFFFFEFF) | N |
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.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | boolean | false | true, false | N |
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.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | boolean | true | true, false | N |
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.
| Effective Version | Type/Units | Default | Range/Values | Restart Type |
|---|---|---|---|---|
| NDB 7.2.0 | unsigned | [none] | 0 - 4294967039 (0xFFFFFEFF) | N |
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.