Key must be the last element in the path – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

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Briefly, this error occurs when the “_key” is not placed at the end of the path in an Elasticsearch query. Elasticsearch expects “_key” to be the last element in the path for correct parsing and execution. To resolve this issue, you should review your Elasticsearch query and ensure that “_key” is placed at the end of the path. Also, check for any syntax errors or misplaced elements in your query.

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This guide will help you check for common problems that cause the log ” _key must be the last element in the path ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: search, aggregations.

Log Context

Log “_key must be the last element in the path” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 throw new InvalidAggregationPathException("_count must be the last element in the path");
 return getDocCount();
 } else if (aggName.equals("_key")) {
 if (path.size() > 1) {
 throw new InvalidAggregationPathException("_key must be the last element in the path");
 return getKey();
 InternalAggregation aggregation = aggregations.get(aggName);
 if (aggregation == null) {


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