Parallelism - Upstash Documentation

The parallelism limit controls the maximum number of calls that can be executed concurrently. Unlike rate limiting (which works per time window), parallelism enforces concurrency control with a token-based system.

Configure Retry Attempt Count

import { Client } from "@upstash/workflow";

const client = new Client({ token: "<QSTASH_TOKEN>" })

const { workflowRunId } = await client.trigger({
  url: "https://<YOUR_WORKFLOW_ENDPOINT>/<YOUR-WORKFLOW-ROUTE>",
  flowControl: {
    key: "user-signup",
    parallelism: 10,
  }
  applyConfiguration: true,
})

Example: If parallelism = 3, at most 3 requests can run concurrently. When tokens are available, requests acquire one and start execution:

A failing step is automatically retried three times

When all tokens are in use, additional requests are not failed — they’re queued in a waitlist:

A failing step is automatically retried three times

The step in the waitlist will wait for a step to complete and hand off it’s token to a pending request:

Token handoff does not guarantee strict ordering. A later request in the waitlist may acquire a token before an earlier one.

A failing step is automatically retried three times

Monitoring

You can monitor wait list size of your flow control key’s using the REST API.

curl -X GET https://qstash.upstash.io/v2/flowControl/YOUR_FLOW_CONTROL_KEY \
  -H "Authorization: Bearer <token>"

It will return the wait list size. In case you request all flow-control keys, it is an array response.

flowControlKey

string

The identifier for your flow control configuration

waitListSize

number

Number of steps waiting to be executed due to parallelism limits

Adding a dashboard to list and manage flow control key’s is on our roadmap.

Workflow

​Monitoring

Monitoring