Why this change is needed:
Two critical issues were identified in Codex review of PR #2391:
1. Migration fails when legacy collections/tables use different embedding dimensions
(e.g., upgrading from 1536d to 3072d models causes initialization failures)
2. When model_suffix is empty (no model_name provided), table_name equals legacy_table_name,
causing Case 1 logic to delete the only table/collection on second startup
How it solves it:
- Added dimension compatibility checks before migration in both Qdrant and PostgreSQL
- PostgreSQL uses two-method detection: pg_attribute metadata query + vector sampling fallback
- When dimensions mismatch, skip migration and create new empty table/collection, preserving legacy data
- Added safety check to detect when new and legacy names are identical, preventing deletion
- Both backends log clear warnings about dimension mismatches and skipped migrations
Impact:
- lightrag/kg/qdrant_impl.py: Added dimension check (lines 254-297) and no-suffix safety (lines 163-169)
- lightrag/kg/postgres_impl.py: Added dimension check with fallback (lines 2347-2410) and no-suffix safety (lines 2281-2287)
- tests/test_no_model_suffix_safety.py: New test file with 4 test cases covering edge scenarios
- Backward compatible: All existing scenarios continue working unchanged
Testing:
- All 20 tests pass (16 existing migration tests + 4 new safety tests)
- E2E tests enhanced with explicit verification points for dimension mismatch scenarios
- Verified graceful degradation when dimension detection fails
- Code style verified with ruff and pre-commit hooks
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