Altering A Running Graph

Nothing built so far required tearing anything down — every step added nodes. ALTER statements change what already exists: junction logic, relay properties, schemas, ingestor sources, emitter sinks, stateful processor behavior, reingestor wiring, and generator cadence or routes. Nervix classifies each validated change and pauses as little as possible — the statement result reports the executed level (ALTER Lock And Quiesce Classification):

• DYNAMIC — hot-applied; nothing pauses (relay capacity, junction filters and route logic, deduplicator or reorderer MAX TIME, emitter flush policy)
• ENTITY_PAUSE — only the affected node or relay is gated and drained (topology changes, deduplication keys, reorderer ordering, ingestor, reingestor, generator, and emitter reconfiguration, relay materialized state — the ALTER RELAY in Generators ran at this level)
• DOMAIN_PAUSE — domain ingestion stops, in-flight work drains, the new graph is installed atomically, and flow resumes (schema and branching changes)

Before altering anything, SHOW CREATE <kind> <name>; prints the current canonical definition.

Change Routing Logic — Dynamic

Lower the high-value threshold from 1000 to 500. Route changes go through ALTER JUNCTION; REPLACE ROUTE requires the complete route body, not a diff:

ALTER JUNCTION route_orders
  REPLACE ROUTE TO high_value_orders
    INHERIT ALL
    SET tier = CASE
          WHEN input.amount >= 10000 THEN "vip"
          ELSE "high"
        END
    WHERE output.amount >= 500
    FLUSH IMMEDIATE
    ON MESSAGE ERROR LOG;

The result reports quiesce level: DYNAMIC — the domain never paused, buffered work stayed in place, and the very next order is evaluated against the new threshold. Produce a 700-amount order and watch it reach high_value_out, which the old threshold would have dropped.

Relay capacity is equally uneventful (Altering Relays, capacity semantics under Capacity):

ALTER RELAY orders SET CAPACITY 8;

Evolve A Schema — Domain Pause

Payments gain a method. A codec requires its wire schema to exactly match the internal schema, so both must change in one transaction — the registry validates the complete candidate graph before anything applies (Altering Schemas):

BEGIN;

ALTER WIRE JSON SCHEMA payment_wire
  ADD FIELD method string OPTIONAL;

ALTER SCHEMA payment_record
  ADD FIELD method STRING OPTIONAL;

COMMIT;

This reports quiesce level: DOMAIN_PAUSE: ingestion stops, buffered output is force-flushed (no in-flight records are lost), the graph is swapped, and flow resumes — there is no user-facing PAUSE statement, and a drain timeout rolls the whole batch back (Automatic Model-Alteration Quiescing).

Add the field as OPTIONAL: old payloads without it keep decoding, and the field finalizes as a typed null. Verify by POSTing a payment with "method":"card" to /payments and watching the payments relay.

Two rules worth knowing before you lean on this:

• One alteration at a time per domain — a concurrent mutation is rejected with already has a model alteration in progress, not queued.
• DROP plus CREATE of the same entity in one batch is compared as one modification — you cannot sneak a schema change past domain quiescing by recreating the relay.

Ingestors and emitters have their own operation sets — Altering Ingestors (an ingestor’s ALTER repeats its connector and entity, such as ALTER KAFKA TOPIC INGESTOR kafka_orders, and every ingestor change is entity-pause) and Altering Emitters (flush changes are dynamic; sink, client, and codec changes are entity-pause; source-list membership changes are domain-pause). Processor operations are covered under Altering Deduplicators, Altering Reorderers, Altering Reingestors, and Altering Generators.

Next: run the graph on a logical clock in Paced Domains.