## Summary The main Advanced Search index mapping declares a `join_field` (type `join`) with relation `project: [issue, merge_request, milestone, note, blob, wiki_blob, commit]`, but no search reads it anymore. Project documents have also moved to their own index, so the join has no parent documents in the main index. This removes the dead read path, stops writing the field, and strips it from stored documents, so the mapping can drop it at the next main-index reindex. **Scope: main index only.** This issue removes `join_field` from the main combined Advanced Search index (`gitlab-production`, mapping in `ee/lib/elastic/latest/config.rb`). It is the only index mapping that declares `join_field`, so the separate indices (work items, merge requests, notes, projects, commits, wikis, users, etc.) are not changed and don't need a reindex. This issue covers the code changes and stripping the field from stored documents, none of which needs a reindex. Dropping the field from the mapping happens in the main-index reindex in #600600, which this issue blocks. ## Current state - Mapping: `ee/lib/elastic/latest/config.rb`. - Dead read path: the only `has_parent` query is in `Elastic::Latest::ApplicationClassProxy#project_ids_filter`. It's only reached through `#authorization_filter`, which has no callers since the git class proxy moved to shared filters in eaf8adc0a452 ("Remove search_query_authorization_refactor feature flag"). - Active searches all skip the join: - `Search::Elastic::QueryBuilder#base_options` sets `no_join_project: true` for every query-builder search, including milestones. - Commits are in their own index (`Elastic::Latest::CommitConfig.index_name`); commit search sets `no_join_project: true`. - Blob search sets it from `GitClassProxy#disable_project_joins_for_blob?`, which returns `true` unconditionally. - Note search sets `no_join_project: true`. - No `has_child` queries exist. - Project documents are in a separate index (`Project.use_separate_indices?` is true), routed by `n_<root_ancestor_id>`. - Writers from Rails: `ApplicationInstanceProxy#generic_attributes` adds `join_field` whenever `es_parent` is present. Today that means milestones only: project milestones (parent `project_<id>`) and, since !257456, group milestones (parent `n_<root_ancestor_id>`). Merge requests and notes strip it (`super.except('join_field')`). Snippets have no `es_parent`. - Deletes don't use it: `ElasticDeleteProjectWorker#remove_children_documents` deletes by `project_id` / `rid` / `commit.rid` / `target_project_id` terms with project routing. - `gitlab-elasticsearch-indexer` (Go, separate repo) writes `join_field` on every blob document (`internal/mode/advanced/indexer/indexer.go`). Routing doesn't depend on it: the indexer sets `project_<id>` routing separately (`routingFor` in `internal/mode/advanced/elastic/client.go`). ## Tasks - [x] Remove the dead join path in `ApplicationClassProxy`: `#authorization_filter`, `#should_use_project_ids_filter?`, `#project_ids_filter`, `#project_ids_query` and `#pick_projects_by_membership` have no callers outside that chain. Then remove the `no_join_project` plumbing that only existed to switch the join off, and update the comment in `ee/lib/gitlab/elastic/search_results.rb` that points to `project_ids_query`. - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/259063. Removes the whole unused chain, plus helpers only it used. `no_join_project` stays, because it also controls the doc type filter that snippet search needs. - [x] Stop writing `join_field` from Rails: drop it from `ApplicationInstanceProxy#generic_attributes`, then remove the `except('join_field')` overrides in the merge request and note proxies. - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/259064 - [ ] Stop the Go indexer writing `join_field` for blobs, and update its test mapping (`defaultIndexMapping` in `internal/mode/advanced/elastic/index.go`). - https://gitlab.com/gitlab-org/gitlab-elasticsearch-indexer/-/merge_requests/947. Then bump `GITLAB_ELASTICSEARCH_INDEXER_VERSION` in gitlab-org/gitlab after the indexer release. - [ ] Strip `join_field` from stored documents with a `MigrationRemoveFieldsHelper` migration (`update_by_query` with `ctx._source.remove`), after both writers have stopped. Local testing showed this works while the join mapping still exists and keeps routing (see the 2026-10-01 comment on #600600). - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/261846. A standalone migration rather than `MigrationRemoveFieldsHelper`, because the helper handles one document type and `join_field` is on both blob and milestone documents. Merge after `GITLAB_ELASTICSEARCH_INDEXER_VERSION` is bumped to 5.14.18 (gitlab-org/gitlab-elasticsearch-indexer!960), so blobs don't get the field back. - [ ] Confirm the `exists` count for `join_field` is 0 on staging and production, so #600600 can drop it from the mapping. ## Notes - Existing documents keep the field until they're rewritten. That's harmless while the mapping still has it, but they must be stripped before #600600 drops it from the mapping: the mapping is `dynamic: 'strict'` and the reindex copies `_source` as-is, so any document that still has `join_field` fails its slice and the reindex aborts on the document count check. - Came up in #428589 (group milestones in Advanced Search).