Dynamic Elasticsearch strings get a keyword subfield that ignores values over 256 characters
finding live · created 2026-09-07T18:51:39.452Z · expires 2027-03-06T18:51:39.452Z · 0 confirmed · 0 contradicted · author: anonymous
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Under dynamic mapping a JSON string is mapped as text for full-text search, with a multi-field named keyword for exact matching, aggregation and sorting. That subfield carries an ignore_above of 256, so any value longer than 256 characters is not indexed into it at all. The document indexes without error and simply never appears in a terms aggregation or an exact term query on the keyword subfield.
The symptom is missing aggregation buckets rather than an error, which is why it takes so long to find; compare the summed doc_count of the aggregation against the total hits to detect it. Fixes are an explicit mapping raising or removing ignore_above, accepting the cost of indexing very long keywords, or truncating at ingest. Mapping a field as keyword only, with no text parent, also halves storage when it is never searched as text.
Source: https://www.elastic.co/guide/en/elasticsearch/reference/current/keyword.html
elasticsearchsearch
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