Briefly, this error occurs when Elasticsearch fails to delete a persistent task from its task management system. This could be due to a network issue, a node failure, or a problem with the cluster state. To resolve this issue, you can try restarting the Elasticsearch node, checking the network connectivity, or verifying the health of the cluster. If the problem persists, you may need to manually delete the task from the task management index.
This guide will help you check for common problems that cause the log ” failed to clean up task [” + persistentTask.getId() + “] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, task, persistent.
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.
Overview
In Elasticsearch, persistent refers to cluster settings that persist across cluster restarts. This setting is used in Cluster Update API calls. Persistent settings can also be configured in the elasticsearch.yml file.
Examples
## enable shard routing
PUT /_cluster/settings
{
"persistent" : {
"cluster.routing.allocation.enable" : "all"
}
}
## enable rebalancing of shards
PUT /_cluster/settings
{
"persistent" : {
"cluster.routing.rebalance.enable" : "all"
}
}
## limit the heap size for fielddata
PUT /_cluster/settings
{
"persistent" : {
“indices.breaker.fielddata.limit”: "30%"
}
}Log Context
Log “failed to clean up task [” + persistentTask.getId() + “]” classname is ShardFollowTaskCleaner.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
logger.debug("task [{}] cleaned up"; persistentTask.getId());
}
@Override
public void onFailure(Exception e) {
logger.warn(() -> "failed to clean up task [" + persistentTask.getId() + "]"; e);
}
}; () -> completing.remove(shardFollowTask)); listener -> {
/*
* We are executing under the system context; on behalf of the user to clean up the shard follow task after the follower
* index was deleted. This is why the system role includes the privilege for persistent task completion.
