Dbos Python

DBOS for Python

DBOS provides durable execution so you can write programs that are resilient to any failure. When interrupted, workflows automatically resume from their last completed step. Uses PostgreSQL or SQLite as its system database.

Core Decorators

Essential Patterns

Basic Application Structure

import os
from dbos import DBOS, DBOSConfig

config: DBOSConfig = {
    "name": "my-app",
    "system_database_url": os.environ.get("DBOS_SYSTEM_DATABASE_URL"),
}
DBOS(config=config)

@DBOS.step()
def call_external_api(data: str) -> dict:
    response = requests.post("https://api.example.com", json={"data": data})
    return response.json()

@DBOS.step()
def process_result(result: dict) -> str:
    return result.get("status", "unknown")

@DBOS.workflow()
def my_workflow(input_data: str) -> str:
    api_result = call_external_api(input_data)
    status = process_result(api_result)
    return status

if __name__ == "__main__":
    DBOS.launch()
    result = my_workflow("hello")

Steps with Retry Configuration

@DBOS.step(retries_allowed=True, max_attempts=10)
def unreliable_api_call(url: str) -> str:
    response = requests.get(url)
    response.raise_for_status()
    return response.text

Database Transactions

from sqlalchemy import Table, Column, String, MetaData

metadata = MetaData()
users = Table("users", metadata,
    Column("id", String, primary_key=True),
    Column("name", String),
)

@DBOS.transaction()
def create_user(user_id: str, name: str) -> None:
    DBOS.sql_session.execute(
        users.insert().values(id=user_id, name=name)
    )

@DBOS.transaction()
def get_user(user_id: str) -> dict:
    result = DBOS.sql_session.execute(
        users.select().where(users.c.id == user_id)
    ).fetchone()
    return dict(result) if result else None

@DBOS.workflow()
def user_workflow(user_id: str, name: str) -> dict:
    create_user(user_id, name)
    return get_user(user_id)

Background Workflows

from dbos import WorkflowHandle

@DBOS.workflow()
def background_workflow(data: str) -> str:
    return long_running_task(data)

# Start without blocking
handle: WorkflowHandle = DBOS.start_workflow(background_workflow, "input")
print(f"Workflow ID: {handle.workflow_id}")

# Later, retrieve result
result = handle.get_result()

Queue-Based Processing

from dbos import Queue

queue = Queue("task_queue", worker_concurrency=5)

# Or with rate limiting
rate_limited_queue = Queue(
    "api_queue",
    limiter={"limit": 100, "period": 60}  # 100 requests per minute
)

@DBOS.workflow()
def process_task(task_id: int) -> str:
    return f"Completed task {task_id}"

# Enqueue work
handle = queue.enqueue(process_task, 123)
result = handle.get_result()

Queue with Partitioning

queue = Queue("user_queue", worker_concurrency=10)

@DBOS.workflow()
def process_user_action(user_id: str, action: dict) -> str:
    return f"Processed {action} for {user_id}"

# Actions for same user_id processed in order
queue.enqueue(process_user_action, "user_123", {"type": "update"},
              partition_key="user_123")

Workflow Communication - Messages

@DBOS.workflow()
def checkout_workflow(order_id: str) -> str:
    # Wait up to 5 minutes for payment confirmation
    payment_result = DBOS.recv(topic="payment", timeout_seconds=300)

    if payment_result is None:
        return "payment_timeout"
    if payment_result["status"] == "completed":
        return "order_completed"
    return "payment_failed"

def payment_webhook(workflow_id: str, status: str):
    DBOS.send(workflow_id, {"status": status}, topic="payment")

Workflow Communication - Events

@DBOS.workflow()
def checkout_workflow(order: dict) -> str:
    payment_url = generate_payment_url(order)
    DBOS.set_event("payment_url", payment_url)
    return "completed"

def checkout_handler(order: dict):
    handle = DBOS.start_workflow(checkout_workflow, order)
    url = DBOS.get_event(handle.workflow_id, "payment_url", timeout_seconds=30)
    return {"redirect_url": url}

Durable Sleep

@DBOS.workflow()
def scheduled_task_workflow(delay_seconds: int, task: str) -> str:
    DBOS.sleep(delay_seconds)
    return execute_task(task)

Scheduled Workflows (Cron)

@DBOS.scheduled("0 2 * * *")  # Daily at 2:00 AM
@DBOS.workflow()
def daily_backup(scheduled_time, actual_time):
    perform_backup()
    return "backup_completed"

@DBOS.scheduled("*/15 * * * *")  # Every 15 minutes
@DBOS.workflow()
def health_check(scheduled_time, actual_time):
    return check_system_health()

if __name__ == "__main__":
    DBOS.launch()  # Schedules start automatically

Idempotent Workflows

from dbos import SetWorkflowID

@DBOS.workflow()
def process_payment(payment_id: str, amount: float) -> str:
    return "processed"

def handle_payment(payment_id: str, amount: float):
    # Same workflow ID = same execution (prevents duplicates)
    with SetWorkflowID(f"payment-{payment_id}"):
        result = process_payment(payment_id, amount)
    return result

Workflow Timeout

from dbos import SetWorkflowTimeout

@DBOS.workflow()
def long_workflow(data: str) -> str:
    return "completed"

# Workflow times out after 1 hour
with SetWorkflowTimeout(3600):
    result = long_workflow("input")

Debouncing

from dbos import Debouncer

@DBOS.workflow()
def process_user_input(user_id: str, final_input: str) -> str:
    return f"Processing: {final_input}"

debouncer = Debouncer.create(process_user_input)

def on_user_keystroke(user_id: str, current_input: str):
    debouncer.debounce(user_id, 60, current_input)

Async Workflows

import aiohttp

@DBOS.step()
async def async_fetch(url: str) -> str:
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as resp:
            return await resp.text()

@DBOS.workflow()
async def async_workflow(urls: list[str]) -> list[str]:
    await DBOS.sleep_async(1)
    results = []
    for url in urls:
        result = await async_fetch(url)
        results.append(result)
    return results

FastAPI Integration

from fastapi import FastAPI
import uvicorn

app = FastAPI()

@DBOS.step()
def process_order(order_id: str) -> dict:
    return {"order_id": order_id, "status": "processed"}

@app.post("/orders/{order_id}")
@DBOS.workflow()
def create_order(order_id: str) -> dict:
    return process_order(order_id)

@app.get("/orders/{order_id}/status")
def get_order_status(order_id: str):
    workflows = DBOS.list_workflows(workflow_id=order_id)
    return workflows[0] if workflows else None

if __name__ == "__main__":
    DBOS.launch()
    uvicorn.run(app, host="0.0.0.0", port=8000)

Class-Based Workflows

from dbos import DBOSConfiguredInstance

@DBOS.dbos_class()
class DataProcessor(DBOSConfiguredInstance):
    def __init__(self, source_url: str):
        self.source_url = source_url
        super().__init__(config_name=source_url)

    @DBOS.step()
    def fetch_data(self) -> dict:
        return requests.get(self.source_url).json()

    @DBOS.workflow()
    def process(self) -> dict:
        data = self.fetch_data()
        return {"transformed": data}

# Instantiate before DBOS.launch()
processor = DataProcessor("https://api.example.com/data")

if __name__ == "__main__":
    DBOS.launch()
    result = processor.process()

Workflow Introspection

# List workflows by status
pending = DBOS.list_workflows(status="PENDING", limit=10)
completed = DBOS.list_workflows(status="SUCCESS", sort_desc=True)

# Get workflow steps
steps = DBOS.list_workflow_steps(workflow_id)

# Control operations
DBOS.cancel_workflow(workflow_id)
DBOS.resume_workflow(workflow_id)
DBOS.fork_workflow(workflow_id, start_step=3)

Testing

import pytest
from dbos import DBOS, DBOSConfig

@pytest.fixture()
def dbos_test():
    DBOS.destroy()
    config: DBOSConfig = {"name": "test-app"}
    DBOS(config=config)
    DBOS.reset_system_database()
    DBOS.launch()
    yield
    DBOS.destroy()

def test_workflow(dbos_test):
    result = my_workflow("test_input")
    assert result == "expected_output"

Critical Rules

Determinism Requirements

1. No direct randomness - Wrap in steps
2. No direct time access - Use DBOS.sleep() or wrap in steps
3. No direct I/O - All API calls, file access must be steps
4. No threads in workflows - Use queues or child workflows

Step Requirements

• Inputs and outputs must be serializable (JSON-compatible)
• Should be idempotent when possible
• Use retries_allowed=True for transient failures

Workflow Requirements

• Must be decorated with @DBOS.workflow()
• Input parameters must be serializable
• Return value must be serializable
• Call DBOS.launch() before executing workflows

Transaction Requirements

• Only use @DBOS.transaction() for database operations
• Works with PostgreSQL via SQLAlchemy
• Access database via DBOS.sql_session

Configuration Options

config: DBOSConfig = {
    "name": "my-app",
    "system_database_url": "postgresql://...",
    "application_database_url": "postgresql://...",
    "log_level": "INFO",
    "application_version": "1.0.0",
}