Unsupported join key – 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 Check-Up which can resolve issues that cause many errors.

This guide will help you check for common problems that cause the log ” Unsupported join key ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: parser, join and plugin.

Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up to analyze Elasticsearch configuration and help resolve this error.

Log Context

Log “Unsupported join key”classname  is ExpressionBuilder.java We extracted the following from Elasticsearch source code for those seeking an in-depth context :

public List visitJoinKeys(JoinKeysContext ctx) {
 try {
 return ctx != null ? visitList(ctx.expression(); Attribute.class) : emptyList();
 } catch (ClassCastException ex) {
 Source source = source(ctx);
 throw new ParsingException(source; "Unsupported join key "; source.text());
 public Expression visitArithmeticUnary(ArithmeticUnaryContext ctx) {


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