Transactional Outbox & Compensation Machine

How an order service guarantees eventual consistency across payment and inventory boundaries

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2D Architecture Machine DSL

VALID · 4 s

canvas 18 10
register api "Order API" at 0.6 1.2 size 4.2 2.2 value "POST /orders" tone accent
memory db "Orders + Outbox SQL" at 6.2 0.8 size 5.4 4.2 cells 4 start 1 stride 1
stack relay "CDC Outbox Queue" at 6.2 5.8 size 5.4 3.4
register payment "Payment Gateway" at 13.2 1.2 size 4.2 2.2 value "IDLE"
register inventory "Inventory Hold" at 13.2 6.2 size 4.2 2.2 value "HELD 1 UNIT" tone accent
arrow txWrite from api to db label "BEGIN / COMMIT"
arrow cdcTail from db to relay label "WAL tail"
arrow payRpc from relay to payment label "charge"
arrow compensate from relay to inventory label "release" tone warning hidden

step "Atomic Local Commit"
  caption "Order row and Outbox event commit inside one ACID database transaction"
  highlight api
  highlight db
  flow txWrite label "TX 804"
  write db 0 "ord_804: PENDING"
  write db 1 "outbox: OrderCreated"
  tone db accent

step "CDC Tail & Dispatch"
  caption "The outbox relay tails committed WAL entries and dispatches the payment command"
  flow cdcTail label "binlog seq 41"
  push relay "evt: OrderCreated"
  highlight relay
  flow payRpc label "auth 129 USD"
  set payment value "VERIFYING"

step "Downstream Decline"
  caption "Payment gateway rejects the card, enqueueing a deterministic saga compensation"
  flow payRpc reverse label "402 Declined"
  set payment value "402 DECLINED"
  tone payment danger
  highlight payment
  push relay "cmd: CompensateHold"
  tone relay warning

step "Compensating Rollback"
  caption "Saga worker releases the inventory reservation and marks order 804 cancelled"
  show compensate
  flow compensate label "release hold"
  pop relay
  pop relay
  write db 0 "ord_804: CANCELLED"
  write db 2 "outbox: SagaRolledBack"
  set inventory value "RELEASED OK"
  tone inventory success
  tone relay normal

DSL Grammar Quick Reference

canvas 18 10
register id "Label" at X Y size W H value "Val" [tone accent]
box id "Label" at X Y size W H [tone muted]
memory id "Label" at X Y size W H cells 4
stack id "Label" at X Y size W H
arrow id from srcId to dstId [label "Text"]
step "Step Title"
  caption "Shown beneath stage"
  highlight id | flow arrowId [reverse] [label "msg"]
  set id value "New" | write memId 0 "cell" | push stackId "item"
  tone id normal|muted|accent|success|warning|danger

Narrative Cues & Prose (4)

Cue 1

Cue 2

Cue 3

Cue 4

Live Stage Timeline & Scrub Preview0 s / 4 s

Active Beat · Cue 1 (1 s)

1. Single-Database Atomic Write

Instead of dual-writing to SQL and a message broker, the Order API writes both the pending order row and an outbox event record inside one local ACID transaction.