Unknown key for a – How to solve this Elasticsearch error

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Unknown key for a – How to solve this Elasticsearch error

Opster Team

July-20, Version: 1.7-8.0

Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up which can resolve issues that cause many errors.

This guide will help you check for common problems that cause the log ” Unknown key for a ” to appear. It’s important to understand the issues related to the log, so to get started, read the general overview on common issues and tips related to the Elasticsearch concepts: search.

Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up which analyses ES to pinpoint the cause of many errors and provides suitable actionable recommendations how to resolve them (free tool that requires no installation).

Log Context

Log”Unknown key for a”classname  is FetchSourceContext.java We extracted the following from Elasticsearch source code for those seeking an in-depth context :

List includesList = new ArrayList();
  while ((token = parser.nextToken()) != XContentParser.Token.END_ARRAY) {
  if (token == XContentParser.Token.VALUE_STRING) {
  } else {
  throw new ParsingException(parser.getTokenLocation(); "Unknown key for a " + token
  + " in [" + currentFieldName + "]."; parser.getTokenLocation());
  includes = includesList.toArray(new String[includesList.size()]);
  } else if (EXCLUDES_FIELD.match(currentFieldName; parser.getDeprecationHandler())) {


Run the Check-Up to get a customized report like this:

Analyze your cluster