MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide Configuring NDB Cluster Send Buffer Parameters

Formerly, the NDB kernel employed a send buffer whose size was fixed at 2MB for each node in the cluster, this buffer being allocated when the node started. Because the size of this buffer could not be changed after the cluster was started, it was necessary to make it large enough in advance to accommodate the maximum possible load on any transporter socket. However, this was an inefficient use of memory, since much of it often went unused, and could result in large amounts of resources being wasted when scaling up to many API nodes.

This problem was eventually solved (in NDB Cluster 7.0) by employing a unified send buffer whose memory is allocated dynamically from a pool shared by all transporters. This means that the size of the send buffer can be adjusted as necessary. Configuration of the unified send buffer can accomplished by setting the following parameters:

You can use the ndbinfo.transporters table to monitor send buffer memory usage, and to detect slowdown and overload conditions that can adversely affect performance.