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Themembership table describes the view that each data node has of all the others in the cluster, including node group membership, president node, arbitrator, arbitrator successor, arbitrator connection states, and other information.

Themembership table contains the following columns:

Notes

The node ID and node group ID are the same as reported byndb_mgm -e "SHOW".

left_node andright_node are defined in terms of a model that connects all data nodes in a circle, in order of their node IDs, similar to the ordering of the numbers on a clock dial, as shown here:

Figure 25.6 Circular Arrangement of NDB Cluster Nodes

In this example, we have 8 data nodes, numbered 5, 6, 7, 8, 12, 13, 14, and 15, ordered clockwise in a circle. We determine“left” and“right” from the interior of the circle. The node to the left of node 5 is node 15, and the node to the right of node 5 is node 6. You can see all these relationships by running the following query and observing the output:

mysql> SELECT node_id,left_node,right_node    -> FROM ndbinfo.membership;+---------+-----------+------------+| node_id | left_node | right_node |+---------+-----------+------------+|       5 |        15 |          6 ||       6 |         5 |          7 ||       7 |         6 |          8 ||       8 |         7 |         12 ||      12 |         8 |         13 ||      13 |        12 |         14 ||      14 |        13 |         15 ||      15 |        14 |          5 |+---------+-----------+------------+8 rows in set (0.00 sec)

The designations“left” and“right” are used in the event log in the same way.

Thepresident node is the node viewed by the current node as responsible for setting an arbitrator (seeNDB Cluster Start Phases). If the president fails or becomes disconnected, the current node expects the node whose ID is shown in thesuccessor column to become the new president. Thesuccession_order column shows the place in the succession queue that the current node views itself as having.

In a normal NDB Cluster, all data nodes should see the same node aspresident, and the same node (other than the president) as itssuccessor. In addition, the current president should see itself as1 in the order of succession, thesuccessor node should see itself as2, and so on.

All nodes should show the samearb_ticket values as well as the samearb_state values. Possiblearb_state values areARBIT_NULL,ARBIT_INIT,ARBIT_FIND,ARBIT_PREP1,ARBIT_PREP2,ARBIT_START,ARBIT_RUN,ARBIT_CHOOSE,ARBIT_CRASH, andUNKNOWN.

arb_connected shows whether this node is connected to the node shown as this node'sarbitrator.

Theconnected_rank1_arbs andconnected_rank2_arbs columns each display a list of 0 or more arbitrators having anArbitrationRank equal to 1, or to 2, respectively.