25.6.16.44 The ndbinfo membership Table

The membership 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.

The membership table contains the following columns:

• node_id

  This node's node ID

• group_id

  Node group to which this node belongs

• left node

  Node ID of the previous node

• right_node

  Node ID of the next node

• president

  President's node ID

• successor

  Node ID of successor to president

• succession_order

  Order in which this node succeeds to presidency

• Conf_HB_order

  -

• arbitrator

  Node ID of arbitrator

• arb_ticket

  Internal identifier used to track arbitration

• arb_state

  Arbitration state

• arb_connected

  Whether this node is connected to the arbitrator; either of Yes or No

• connected_rank1_arbs

  Connected arbitrators of rank 1

• connected_rank2_arbs

  Connected arbitrators of rank 1

Notes

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

left_node and right_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.

The president node is the node viewed by the current node as responsible for setting an arbitrator (see NDB Cluster Start Phases). If the president fails or becomes disconnected, the current node expects the node whose ID is shown in the successor column to become the new president. The succession_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 as president, and the same node (other than the president) as its successor. In addition, the current president should see itself as 1 in the order of succession, the successor node should see itself as 2, and so on.

All nodes should show the same arb_ticket values as well as the same arb_state values. Possible arb_state values are ARBIT_NULL, ARBIT_INIT, ARBIT_FIND, ARBIT_PREP1, ARBIT_PREP2, ARBIT_START, ARBIT_RUN, ARBIT_CHOOSE, ARBIT_CRASH, and UNKNOWN.

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

The connected_rank1_arbs and connected_rank2_arbs columns each display a list of 0 or more arbitrators having an ArbitrationRank equal to 1, or to 2, respectively.

Note

Both management nodes and API nodes are eligible to become arbitrators.