Pattern 21 — Add a Downstream Dependent Node

Class: Create (new node only) | Test: test_cookbook_21_add_downstream_node

When to use

Add a new stream table that consumes an existing one. Only the new downstream node requires a Create step; the upstream table is unchanged.

New migration file

-- migrations/streams/c21_summary.sql  (new)
-- @aqueduct:schedule = "1m"
-- @aqueduct:depends_on = ["public.c21_totals"]
SELECT COUNT(*) AS n FROM public.c21_totals;

Plan output

  = c21_totals     [unchanged]
  + c21_summary    [create]    new downstream node

Notes

• The existing upstream table (c21_totals) is not touched — zero downtime for consumers reading from it.
• The plan executes the Create step only after confirming the upstream is healthy.