spakky-saga 6.4.0

Distributed transaction saga orchestration for Spakky Framework

spakky-saga

Distributed transaction saga orchestration for Spakky Framework.

Installation

pip install spakky-saga

Features

• @Saga stereotype: Marks saga orchestrator classes (extends @Pod)
• AbstractSaga[SagaDataT]: Generic base class with flow() abstract method and execute() entry point
• @saga_step decorator: Typed descriptor that enables >>, &, | operators on instance methods
• Flow DSL: Declarative composition via operators or builder functions (saga_flow, step, parallel)
• Error strategies: Compensate (default), Skip, Retry(max_attempts, backoff, then) with ExponentialBackoff
• Timeouts: Per-step (timeout=) and per-saga (SagaFlow.timeout())
• Parallel execution: asyncio.gather based groups (& operator / parallel())
• Compensation: Automatic reverse-order rollback of committed steps on failure
• SagaResult[T]: Non-throwing result with status, data, failed_step, error, history, elapsed
• Structured logging: [saga=... step=... status=... elapsed=...ms] format

Quick Start

Define Saga Data

from spakky.saga import AbstractSagaData


class OrderSagaData(AbstractSagaData):
    order_id: int
    customer_id: int
    ticket_id: int | None = None

Define a Saga

from spakky.saga import AbstractSaga, Saga, SagaFlow, saga_step


@Saga()
class CreateOrderSaga(AbstractSaga[OrderSagaData]):
    @saga_step
    async def issue_ticket(self, data: OrderSagaData) -> OrderSagaData:
        ...

    @saga_step
    async def cancel_ticket(self, data: OrderSagaData) -> None:
        ...

    @saga_step
    async def reserve_stock(self, data: OrderSagaData) -> OrderSagaData:
        ...

    def flow(self) -> SagaFlow[OrderSagaData]:
        return SagaFlow(
            items=(
                self.issue_ticket >> self.cancel_ticket,  # Transaction
                self.reserve_stock,                        # SagaStep (no compensation)
            )
        )

Execute

result = await saga.execute(OrderSagaData(order_id=1, customer_id=42))
if result.status is SagaStatus.COMPLETED:
    ...

Builder Function Alternative

from spakky.saga import Retry, parallel, saga_flow, step


flow = saga_flow(
    step(issue_ticket_fn, compensate=cancel_ticket_fn),
    parallel(reserve_stock_fn, charge_payment_fn),
    step(confirm_order_fn, on_error=Retry(max_attempts=3)),
)

Flow Operators

Operator	Meaning	Result Type
>>	Bind compensate function	Transaction[T]
&	Parallel execution	Parallel[T]
|	Attach error strategy	Same as LHS + on_error

Error Strategies

Strategy	Signature	Description
Compensate()	(default)	Trigger reverse-order compensation
Skip()	—	Ignore failure and continue
Retry(max_attempts, backoff, then)	Retry(3, ExponentialBackoff(1.0), Compensate())	Retry N times, then apply then strategy
ExponentialBackoff(base=1.0)	—	base * 2^(attempt-1) delay between retries

API Reference

Stereotype / Base

Symbol	Description
@Saga()	Stereotype for saga orchestrator classes (extends @Pod)
AbstractSaga[SagaDataT]	ABC base with flow() abstract method and execute()
@saga_step	Descriptor decorator enabling >>, &, | operators
AbstractSagaData	Base data model (@immutable + AbstractDomainModel, auto-generates saga_id: UUID)

Flow Types

Symbol	Description
SagaFlow[T]	Top-level flow definition (items, saga_timeout, compensation_failure_handler)
SagaStep[T]	Single action without compensation
Transaction[T]	Action + compensate pair
Parallel[T]	Concurrent group of steps/transactions
FlowItem[T]	Union of flow-composable items
ActionFn[T] / CompensateFn[T]	Type aliases for action / compensate callables
SagaDataT	TypeVar bound to AbstractSagaData

Builders

Function	Description
saga_flow(*items)	Construct a SagaFlow from sequential items
step(action, *, compensate=, on_error=, timeout=)	Build SagaStep or Transaction
parallel(*items)	Build a Parallel group (requires ≥ 2 items)

Execution

Symbol	Description
run_saga_flow(flow, data, *, saga_name=)	Execute a flow; returns SagaResult
AbstractSaga.execute(data)	Thin wrapper over run_saga_flow using type(self).__name__

Result Types

Symbol	Description
SagaResult[T]	status, data, failed_step, error, history, elapsed
StepRecord	name, status, elapsed — per-step execution record
StepStatus	COMMITTED, FAILED, COMPENSATED
SagaStatus	STARTED, RUNNING, COMPENSATING, COMPLETED, FAILED, TIMED_OUT

Errors

Error	Description
AbstractSpakkySagaError	ABC base for all saga errors
SagaFlowDefinitionError	Invalid saga flow definition (static validation)
SagaCompensationFailedError	Compensation failed during rollback
SagaStepTimeoutError	Raised internally when a step exceeds its timeout (routed through on_error)
SagaParallelMergeConflictError	Parallel steps modified the same field during data merge
SagaEngineNotConnectedError	execute() called before the saga engine is connected

Related

• ADR-0007 — Architecture decision record
• spakky-domain — provides AbstractDomainModel (parent of AbstractSagaData)

License

MIT License