Unknown cause – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch encounters an issue that it cannot identify. This is often due to a lack of detailed logging or an unexpected condition in the system. To resolve this issue, you can increase the logging level to get more detailed information about the error. You can also check the health of your Elasticsearch cluster and ensure that all nodes are functioning properly. Additionally, you should verify your query syntax and data types, as incorrect usage can often lead to unknown errors.

This guide will help you check for common problems that cause the log ” unknown cause ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: rest.

Log Context

Log “unknown cause” class name is RestController.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 public void dispatchBadRequest(final RestChannel channel; final ThreadContext threadContext; final Throwable cause) {
 try {
 final Exception e;
 if (cause == null) {
 e = new ElasticsearchException("unknown cause");
 } else if (cause instanceof Exception) {
 e = (Exception) cause;
 } else {
 e = new ElasticsearchException(cause);


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