Added a flattened sink for unmapped fields at RootObjectMapper in columnar index modes#155007
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Added a flattened sink for unmapped fields at RootObjectMapper in columnar index modes#155007Kubik42 wants to merge 1 commit into
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:StorageEngine/Logs
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Jul 24, 2026
| /** | ||
| * Feature flag gating the implicit {@code _unmapped} sink that absorbs unmapped fields on strict columnar indices. | ||
| */ | ||
| public static final FeatureFlag UNMAPPED_FIELDS_FEATURE_FLAG = new FeatureFlag("flattened_unmapped_fields"); |
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Everything is gated behind a feature flag since I plan on splitting the work into multiple PRs for easier reviewing.
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This change is part of the work for https://github.com/elastic/logs-program/issues/149 and implements the beginning of https://github.com/elastic/logs-program/issues/54. What remains is the query, synthetic source, and block loader wiring.
Currently, all unmapped fields are matched with a corresponding
FieldMapper(decided by us or via dynamic templates). The problem with this approach is that it creates a field explosion: forNunmapped fields, we createNfields in Lucene.This PR addresses that by using a flattened field as a root-level sink for all unmapped fields. This works in unison with
subobjects: false(disabled in strictly columnar index modes and not updateable), which flattens the paths to all leaves. All mapped fields are still parsed the same way.Note, https://github.com/elastic/logs-program/issues/54 initially suggested to leverage the mapped sub-fields functionality of
FlattenedFieldMapper, but I believe this is the better option; explanation.