Document mapping type name can t start with found mappingType – How to solve this OpenSearch exception

Opster Team

Aug-23, Version: 1-1.3

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Briefly, this error occurs when the mapping type name of a document in OpenSearch starts with an underscore (_), which is not allowed. OpenSearch uses underscore prefixes for system fields, hence user-defined fields shouldn’t start with an underscore. To resolve this issue, you can rename the mapping type to not start with an underscore. If the mapping type is being automatically generated, check the source of the data to ensure it doesn’t start with an underscore. Alternatively, you can use a script to rename the mapping types before they are sent to OpenSearch.

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This guide will help you check for common problems that cause the log ” Document mapping type name can’t start with ‘_’; found: [” + mappingType + “] ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: metadata, document, cluster, mapping.

Log Context

Log “Document mapping type name can’t start with ‘_’; found: [” + mappingType + “]” class name is We extracted the following from OpenSearch source code for those seeking an in-depth context :

 assert mappingType != null;  if (MapperService.DEFAULT_MAPPING.equals(mappingType) == false
 && MapperService.SINGLE_MAPPING_NAME.equals(mappingType) == false
 && mappingType.charAt(0) == '_') {
 throw new InvalidTypeNameException("Document mapping type name can't start with '_'; found: [" + mappingType + "]");
 Metadata.Builder builder = Metadata.builder(metadata);
 boolean updated = false;
 for (IndexMetadata indexMetadata : updateList) {
 boolean updatedMapping = false;


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