{"id":"map-side-joins-track-mapper-id-on-output","text":"All three map-side join strategies attach a `_mapper_id` field to each output record, enabling verification that partitions/mappers operated independently","truth_value":"IN","source":"entries/2026/05/29/topic-ddia-ch10-reduce-side-joins.md","source_url":"","source_hash":"","justifications":[],"dependents":[],"metadata":{},"explanation":{"steps":[{"node":"map-side-joins-track-mapper-id-on-output","truth_value":"IN","reason":"premise"}]}}