How To Solve Issues Related to Log – Cannot send ban for tasks with the parent to the node

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Updated: Jan-20

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Troubleshooting background

To troubleshoot Elasticsearch log “Cannot send ban for tasks with the parent to the node” it’s important to understand common problems related to Elasticsearch concepts: admin, cluster, node. See detailed explanations below complete with common problems, examples and useful tips.

Cluster in Elasticsearch

What is it

In Elasticsearch a cluster is a collection of one or more nodes (servers / VMs). A cluster can consist of an unlimited number of nodes. The cluster provides interface for indexing and storing data and search capability across all of the data which is stored in the data nodes

Each cluster has a single master node that is elected by the master eligible nodes. In cases where the master is not available the other connected master eligible nodes elect a new master. Clusters are identified by a unique name, which defaults to “Elasticsearch”.

Nodes in Elasticsearch

What it is

Simply explained a node is a single server that is part of a cluster. Each node is assigned with one or more roles, which describes the node responsibility and operations – Data nodes stores the data, and participates in the cluster’s indexing and search capabilities, while master nodes are responsible for managing the cluster activities and storing the cluster state, including the metadata.

While it’s possible to run several Node instances of Elasticsearch on the same hardware, it’s considered a best practice to limit a server to a single running instance of Elasticsearch.

Nodes connect to each other and form a cluster by using a discovery method. 

Roles
Master node

Master nodes are in charge of cluster-wide settings and changes  – deleting or creating indices and fields, adding or removing nodes and allocating shards to nodes. Each cluster has a single master node that is elected from the master eligible nodes using a distributed consensus algorithm and is reelected if the current master node fails.

Coordinator Node (aka client node)

Coordinator Node – is a node that does not hold any configured role. It doesn’t hold data, not part of the master eligible group nor execute ingest pipelines. Coordinator node serves incoming search requests and is acting as the query coordinator – running the query and fetch phases, sending requests to every node which holds a shard being queried. The client node also distributes bulk indexing operations and route queries to shards copies based on the nodes responsiveness.

Task in Elasticsearch

What it is

A task is equivalent to an Elasticsearch operation, which can be any request performed on an Elasticsearch cluster. For example, a delete by query request, a search request and so on. Elasticsearch provides a dedicated Task API for the task management which includes various actions, from retrieving the status of current running tasks to canceling any long running task.

Examples
Get all currently running tasks on all nodes of the cluster

Apart from other information, the response of the below request contains task IDs of all the tasks which can be used to get detailed information about the particular task in question.

GET _tasks
GET detailed information of a particular task

clQFAL_VRrmnlRyPsu_p8A:1132678759 is the ID of the task in below request.

GET _tasks/clQFAL_VRrmnlRyPsu_p8A:1132678759
Get all the current tasks running on particular nodes
GET _tasks?nodes=nodeId1,nodeId2
Cancel a long-running task

clQFAL_VRrmnlRyPsu_p8A:1132678759 is the ID of the task in the below request.

POST /_tasks/clQFAL_VRrmnlRyPsu_p8A:1132678759/_cancel?pretty
Notes
  • The Task API will be most useful when you want to investigate the spike of resource utilization in the cluster or want to cancel an operation.

To help troubleshoot related issues we have gathered selected Q&A from the community and issues from Github , please review the following for further information :

1 Uld Not Resolve From State  

2Tity Framework Self Referencing Loo  


Log Context

Log ”Cannot send ban for tasks with the parent [{}] to the node [{}]” classname is TransportCancelTasksAction.java
We have extracted the following from Elasticsearch source code to get an in-depth context :

                         listener.onResponse(null);
                    }

                    
Override
                    public void handleException(TransportException exp) {
                        logger.warn("Cannot send ban for tasks with the parent [{}] to the node [{}]"; request.parentTaskId; node.key);
                        listener.onFailure(exp);
                    }
                });
        }
    }





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