## What
Fields that are empty in almost all records now show a subtle `Mostly
empty` hint next to their name in the object's Fields settings table
(same visual treatment as `Deactivated`), with a tooltip explaining the
signal and a matching **Mostly empty** toggle in the search filter
dropdown. The goal is to nudge admins to clean up and deactivate fields
nobody uses, while keeping the page untouched when the data model is
healthy.
## How
**No table scans.** Emptiness is read from Postgres planner statistics,
so the cost is a catalog lookup regardless of table size:
- `pg_class.reltuples` gates the feature on an approximate row count (≥
100 records; never-analyzed tables mean no hints). Reuses the shared
helper extracted from `ObjectRecordCountService`.
- `pg_stats.null_frac` plus the sampled frequency of the column type's
empty sentinel (`''` for text columns, `'{}'` for arrays, `'{}'`/`'[]'`
for json — matched per physical column type) gives a per-column empty
fraction. A value dominating ≥ 95% of a column is guaranteed to appear
in the most-common-values list, so the approximation is reliable exactly
at the threshold we care about.
**Decision rules** (pure util, unit-tested):
- Flag when every relevant column is ≥ 95% empty and the object has ≥
100 records.
- Skip system fields, the label identifier, relations, booleans, and
actor fields (exhaustive switch — a new `FieldMetadataType` fails to
compile until classified).
- Composite fields must have all their columns empty, with column sets
derived from `compositeTypeDefinitions`; only default-bearing code
columns (`currencyCode`, phone country/calling codes) are excluded so
stamped defaults don't mask emptiness.
- Anything unknown (missing stats, new column since last ANALYZE)
degrades to silence — no hint is ever shown on missing data.
**API:** one `mostlyEmptyFieldMetadataIds(objectMetadataId)` query on
the metadata schema, guarded by the `DATA_MODEL` settings permission,
fetched lazily when the fields page opens.
**UI:** exception-based — no new columns, no persistent controls. The
badge and the filter toggle only materialize when at least one field
qualifies, and disappear once things are cleaned up.
## Test
- Unit tests for the decision util (threshold,
system/label-identifier/inactive exclusion, missing statistics,
composite all-columns rule, links label/secondary data, currency
narrowing, excluded types).
- Catalog SQL validated against Postgres 16 with a table mimicking
Twenty's column shapes (text `''` defaults, enums, arrays, jsonb,
currency pairs), including the type-aware sentinel matching (a text
column full of literal `"{}"` strings does not count as empty).
- End-to-end on a seeded dev instance: 899 companies with a mix of
filled/empty fields — the API returned exactly the five fields predicted
by the raw statistics (`annualRevenue`, `employees`, `introVideo`,
`tagline`, `workPolicy`) and correctly excluded `address` (city 33%
filled), actor/system fields, and the label identifier.
- UI driven with Playwright: badge, tooltip copy, filter toggle, and
filtered table all verified visually.
- `lint:diff-with-main`, `typecheck` (server + front), and all three
`graphql:generate` configurations + SDK metadata client regenerated and
committed.
Félix Malfait
5e27e04c0a