Elasticsearch mapping explosion — too many fields

Elasticsearch rejects new documents with 'Limit of total fields exceeded'. Index performance degrades as more unique field names are added. Common when indexing dynamic JSON with arbitrary keys.

(1) Set explicit mappings instead of relying on dynamic mapping. (2) Increase limit cautiously: index.mapping.total_fields.limit (default 1000) — but high field counts hurt performance. (3) Use flattened field type for arbitrary JSON: maps entire object as a single field with limited query capability. (4) Use nested type for arrays of objects (instead of dynamic expansion). (5) Disable dynamic mapping for indices with unknown fields: dynamic: false (ignores unmapped fields) or dynamic: strict (rejects them). (6) Consider restructuring data: use a fixed schema with key-value pairs instead of arbitrary field names.

Each unique field in Elasticsearch creates mapping metadata, inverted index entries, and doc values. Thousands of fields consume heap memory and slow queries because the cluster must manage all field metadata.