Unknown key for a – Elasticsearch Error How To Solve Related Issues

Unknown key for a – Elasticsearch Error How To Solve Related Issues

Updated: July-20

Elasticsearch 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 causing 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 discover the cause of many errors and provides suitable actionable recommendations (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())) {

Related issues to this log

We have gathered selected Q&A from the community and issues from Github, that can help fix related issues please review the following for further information :

1 elasticsearch 5: Unknown key for a START_OBJECT in [filters] -views 38,052 ,score 19

Unknown key for a START_OBJECT in [bool] in elastic search -views   7,412,score 8

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