Briefly, this error occurs when Elasticsearch is unable to start a datafeed due to issues with shard allocation. This could be due to insufficient disk space, node failures, or configuration issues. To resolve this, you can check the cluster health and ensure all nodes are functioning properly. If disk space is the issue, consider deleting unnecessary indices or increasing the disk space. If it’s a configuration issue, review and correct your shard allocation settings.
This guide will help you check for common problems that cause the log ” Could not start datafeed; allocation explanation [ ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, allocation.
Log Context
Log “Could not start datafeed; allocation explanation [” class name is TransportStartDatafeedAction.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
if (assignment.equals(DatafeedNodeSelector.AWAITING_JOB_RELOCATION)) {
return true;
}
if (assignment.equals(PersistentTasksCustomMetadata.INITIAL_ASSIGNMENT) == false && assignment.isAssigned() == false) {
// Assignment has failed despite passing our "fast fail" validation
exception = new ElasticsearchStatusException("Could not start datafeed; allocation explanation [" +
assignment.getExplanation() + "]"; RestStatus.TOO_MANY_REQUESTS);
return true;
}
}
DatafeedState datafeedState = (DatafeedState) persistentTask.getState();
