441 Queue Deduplication 71c584da

Deduplicate Queued Workflows

Use deduplication IDs to ensure only one workflow with a given ID is active in a queue at a time.

Incorrect (duplicate workflows possible):

queue = Queue("user_tasks")

@app.post("/process/{user_id}")
def process_for_user(user_id: str):
    # Multiple requests = multiple workflows for same user!
    queue.enqueue(process_workflow, user_id)

Correct (deduplicated by user):

from dbos import Queue, SetEnqueueOptions
from dbos import error as dboserror

queue = Queue("user_tasks")

@app.post("/process/{user_id}")
def process_for_user(user_id: str):
    with SetEnqueueOptions(deduplication_id=user_id):
        try:
            handle = queue.enqueue(process_workflow, user_id)
            return {"workflow_id": handle.get_workflow_id()}
        except dboserror.DBOSQueueDeduplicatedError:
            return {"status": "already processing"}

Deduplication behavior:

• If a workflow with the same deduplication ID is ENQUEUED or PENDING, new enqueue raises DBOSQueueDeduplicatedError
• Once the workflow completes, a new workflow with the same ID can be enqueued
• Deduplication is per-queue (same ID can exist in different queues)

Use cases:

• One active task per user
• Preventing duplicate job submissions
• Rate limiting by entity

Reference: Queue Deduplication