supabase / supabase / 29328303657

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fix(studio): scope table editor introspection CTEs to target table OID (#47894)

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES

## What kind of change does this PR introduce?

Bug fix (performance), plus a regression-guard test suite and docs.

## What is the current behavior?

Studio's introspection queries in `@supabase/pg-meta` do `O(catalog)`
work for per-table requests. On databases with very large catalogs
(hundreds of thousands of relations/constraints — real deployments reach
this) they take tens of seconds per dashboard interaction, trip
`statement_timeout`, and create heavy CPU/memory pressure when several
tabs open concurrently. Two instances of the same bug class:

**1. Table Editor query (`getTableEditorSql`)** — fetches metadata for
ONE table by OID, but five catalog scans are unscoped and only filtered
at the top-level join:

- `primary_keys` CTE — scans all of `pg_index` (`where i.indisprimary`)
- `index_cols` CTE — scans all unique indexes
- `relationships` CTE — scans every FK in `pg_constraint` (and is
scanned twice by the two subplans)
- `uniques` subquery (inside `columns`) — scans all single-column unique
constraints
- `check_constraints` subquery (inside `columns`) — scans all
single-column check constraints

The planner cannot push the outer join qual into grouped / `distinct on`
subqueries, so each is computed over the full catalog and thrown away.
`tables-paginated.ts` was previously rewritten to avoid exactly this
pattern; the single-table query never got the same treatment.

**2. Entity definitions (`getTableDefinitionSql` /
`getEntityDefinitionsSql`)** — the vendored `pg_get_tabledef` plpgsql
function scans the entire `information_schema.columns` view once **per
column** (plus `information_schema.tables` once per call) just to decide
whether a name needs double-quoting — a pure string property of a name
it already holds — and its per-index partial-index lo... (continued)

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