Briefly, this error occurs when an Elasticsearch task is cancelled before it gets a chance to start. This could be due to a variety of reasons such as system overload, slow processing speed, or an abrupt shutdown. To resolve this issue, you can try to reduce the load on your system, increase the processing power, or ensure that tasks are not being prematurely terminated. Additionally, check your task management settings to ensure tasks have enough time to start before they are cancelled.
This guide will help you check for common problems that cause the log ” Task cancelled before it started: ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: task.
Overview
A task is an Elasticsearch operation, which can be any request performed on an Elasticsearch cluster, such as 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
Where 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 task
Where 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.
Log Context
Log “Task cancelled before it started:” class name is TaskManager.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
if (task.getParentTaskId().isSet() && bannedParents.isEmpty() == false) {
final Ban ban = bannedParents.get(task.getParentTaskId());
if (ban != null) {
try {
holder.cancel(ban.reason);
throw new TaskCancelledException("Task cancelled before it started: " + ban.reason);
} finally {
// let's clean up the registration
unregister(task);
}
}
