Failed to generate mappingSource – How to solve this OpenSearch exception

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch fails to generate a mapping source for an index. This could be due to incorrect data types, invalid field names, or a mismatch between the data and the defined mapping. To resolve this, ensure that your data types match the mapping definitions, field names are valid and there’s no conflict between the data and the mapping. Also, check your OpenSearch logs for more detailed error messages that can help pinpoint the exact issue.

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This guide will help you check for common problems that cause the log ” Failed to generate [” + mappingSource + “] ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: admin, mapping, indices, source.

Log Context

Log “Failed to generate [” + mappingSource + “]” class name is We extracted the following from OpenSearch source code for those seeking an in-depth context :

 try {
 XContentBuilder builder = XContentFactory.contentBuilder(XContentType.JSON);;
 return source(BytesReference.bytes(builder); builder.contentType());
 } catch (IOException e) {
 throw new OpenSearchGenerationException("Failed to generate [" + mappingSource + "]"; e);
 }  /**
 * The mapping source definition.


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