The NDB Kernel is the collection of data nodes belonging to a MySQL Cluster. The application programmer can for most purposes view the set of all storage nodes as a single entity. Each data node is made up of three main components:

When an application executes a transaction, it connects to one transaction coordinator on one data node. Usually, the programmer does not need to specify which TC should be used, but in some cases where performance is important, the programmer can provide “hints” to use a certain TC. (If the node with the desired transaction coordinator is down, then another TC will automatically take its place.)

Each data node has an ACC and a TUP which store the indexes and data portions of the database table fragment. Even though a single TC is responsible for the transaction, several ACCs and TUPs on other data nodes might be involved in that transaction's execution.