Node down information

Vertica provides performance optimization when cluster nodes fail by distributing the work of the down nodes uniformly among available nodes throughout the cluster.

When a node in your cluster is down, the query plan identifies which node the query will execute on. To help you quickly identify down nodes on large clusters, EXPLAIN output lists up to six nodes, if the number of running nodes is less than or equal to six, and lists only down nodes if the number of running nodes is more than six.

Note

The node that executes down node queries is not always the same one.

The following table provides more detail:

Node state	EXPLAIN output
If all nodes are up, `EXPLAIN` output indicates `All Nodes`.	`Execute on: All Nodes`
If fewer than 6 nodes are up, `EXPLAIN` lists up to six running nodes.	`Execute on: [node_list].`
If more than 6 nodes are up, `EXPLAIN` lists only non-running nodes.	`Execute on: All Nodes Except [node_list]`
If the node list contains non-ephemeral nodes, the `EXPLAIN` output indicates `All Permanent Nodes`.	`Execute on: All Permanent Nodes`
If the path is being run on the query initiator, the `EXPLAIN` output indicates `Query Initiator`.	`Execute on: Query Initiator`

Examples

In the following example, the down node is v_vmart_node0005, and the node v_vmart_node0006 will execute this run of the query.

=> EXPLAIN SELECT * FROM test;
QUERY PLAN
-----------------------------------------------------------------------------
QUERY PLAN DESCRIPTION:
------------------------------
EXPLAIN SELECT * FROM my1table;
Access Path:
+-STORAGE ACCESS for my1table [Cost: 10, Rows: 2] (PATH ID: 1)
| Projection: public.my1table_b0
| Materialize: my1table.c1, my1table.c2
| Execute on: All Except v_vmart_node0005
+-STORAGE ACCESS for my1table (REPLACEMENT FOR DOWN NODE) [Cost: 66, Rows: 2]
| Projection: public.my1table_b1
| Materialize: my1table.c1, my1table.c2
| Execute on: v_vmart_node0006

The All Permanent Nodes output in the following example fragment denotes that the node list is for permanent (non-ephemeral) nodes only:

=> EXPLAIN SELECT * FROM my2table;
Access Path:
+-STORAGE ACCESS for my2table [Cost: 18, Rows:6 (NO STATISTICS)] (PATH ID: 1)
|  Projection: public.my2tablee_b0
|  Materialize: my2table.x, my2table.y, my2table.z
|  Execute on: All Permanent Nodes