MySQL Cluster attempts to use the shared memory transporter and
configure it automatically where possible. (In very early
versions of MySQL Cluster, shared memory segments functioned
only when the server binary was built using
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
other parameters have default values that should work well in
SHM functionality is considered experimental only. It is not officially supported in any current MySQL 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.
To identify a connection between two nodes it is necessary
to provide node identifiers for each of them, as
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 hostnames or IP addresses.
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.
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.
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
This parameter is a boolean
N) parameter which
is disabled by default. When it is enabled, checksums for
all messages are calculated before being placed in the send
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.
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 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
default] section of the