Merging Reducing the aggregations failed when computing the aggregation – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-7.15

Briefly, this error occurs when Elasticsearch is unable to compute the specified aggregation due to issues like memory constraints, incorrect aggregation syntax, or incompatible data types. To resolve this, you can increase the heap size to provide more memory, ensure the aggregation syntax is correct, or check the data types being aggregated to ensure compatibility. Additionally, consider simplifying your aggregation if it’s too complex or breaking it down into smaller, manageable parts.

This guide will help you check for common problems that cause the log ” Merging/Reducing the aggregations failed when computing the aggregation [ ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: aggregations, search.

Log Context

Log “Merging/Reducing the aggregations failed when computing the aggregation [” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 if (referenceTerms != null &&
 referenceTerms.getClass().equals(terms.getClass()) == false &&
 terms.getClass().equals(UnmappedRareTerms.class) == false) {
 // control gets into this loop when the same field name against which the query is executed
 // is of different types in different indices.
 throw new AggregationExecutionException("Merging/Reducing the aggregations failed when computing the aggregation ["
 + referenceTerms.getName() + "] because the field you gave in the aggregation query existed as two different "
 + "types in two different indices");
 for (B bucket : terms.getBuckets()) {
 List bucketList = buckets.computeIfAbsent(bucket.getKey(); k -> new ArrayList<>());