# Queues

The queue concept in QStash allows ordered delivery (FIFO).
See the [API doc](/qstash/api-reference/queues/list-queues) for the full list of related Rest APIs.
Here we list common use cases for Queue and how to use them.

## Ordered Delivery

With Queues, the ordered delivery is guaranteed by default. 
This means:

- Your messages will be queued without blocking the REST API and sent one by one in FIFO order. Queued means [CREATED](/qstash/howto/debug-logs) event will be logged.
- The next message will wait for retries of the current one if it can not be delivered because your endpoint returns non-2xx code. 
  In other words, the next message will be [ACTIVE](/qstash/howto/debug-logs) only after the last message is either [DELIVERED](/qstash/howto/debug-logs) or 
  [FAILED](/qstash/howto/debug-logs). 
- Next message will wait for [callbacks](/qstash/features/callbacks#what-is-a-callback) or [failure callbacks](/qstash/features/callbacks#what-is-a-failure-callback) to finish.

<CodeGroup>

```bash cURL
curl -XPOST -H 'Authorization: Bearer XXX' \
            -H "Content-type: application/json" \
  'https://qstash.upstash.io/v2/enqueue/my-queue/https://example.com' -d '{"message":"Hello, World!"}'
```

```typescript TypeScript
const client = new Client({ token: "<QSTASH_TOKEN>" });

const queue = client.queue({
  queueName: "my-queue"
})

await queue.enqueueJSON({
  url: "https://example.com",
  body: {
    "Hello": "World"
  }
})
```

```python Python
from qstash import QStash

client = QStash("<QSTASH_TOKEN>")
client.message.enqueue_json(
    queue="my-queue",
    url="https://example.com",
    body={
        "Hello": "World",
    },
)
```
</CodeGroup>

## Controlled Parallelism

<Warning>
For the parallelism limit, we introduced an easier and less limited API with publish. 
Please check the [Flow Control](/qstash/features/flowcontrol) page for the detailed information.

Setting parallelism with queues will be deprecated at some point.
</Warning>

To ensure that your endpoint is not overwhelmed and also you want more than one-by-one delivery for better throughput, 
you can achieve controlled parallelism with queues. 

By default, queues have parallelism 1. 
Depending on your [plan](https://upstash.com/pricing/qstash), you can configure the parallelism of your queues as follows:

<CodeGroup>

```bash cURL
curl -XPOST https://qstash.upstash.io/v2/queues/ \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{
    "queueName": "my-queue", 
    "parallelism": 5,
  }'
```

```typescript TypeScript
const client = new Client({ token: "<QSTASH_TOKEN>" });

const queue = client.queue({
  queueName: "my-queue"
})

await queue.upsert({
  parallelism: 1,
})
```

```python Python
from qstash import QStash

client = QStash("<QSTASH_TOKEN>")
client.queue.upsert("my-queue", parallelism=5)
```

</CodeGroup>

After that, you can use the `enqueue` path to send your messages. 

<CodeGroup>

```bash cURL
curl -XPOST -H 'Authorization: Bearer XXX' \ 
            -H "Content-type: application/json" \
  'https://qstash.upstash.io/v2/enqueue/my-queue/https://example.com' -d '{"message":"Hello, World!"}'
```

```typescript TypeScript
const client = new Client({ token: "<QSTASH_TOKEN>" });

const queue = QStashClient.queue({
  queueName: "my-queue"
})

await queue.enqueueJSON({
  url: "https://example.com",
  body: {
    "Hello": "World"
  }
})
```

```python Python
from qstash import QStash

client = QStash("<QSTASH_TOKEN>")
client.message.enqueue_json(
    queue="my-queue",
    url="https://example.com",
    body={
        "Hello": "World",
    },
)
```
</CodeGroup>

You can check the parallelism of your queues with the following API:

<CodeGroup>
```bash cURL
curl https://qstash.upstash.io/v2/queues/my-queue \
  -H "Authorization: Bearer <token>"
```

```typescript TypeScript
const client = new Client({ token: "<QSTASH_TOKEN>" });

const queue = client.queue({
  queueName: "my-queue"
})

const res = await queue.get()
```

```python Python
from qstash import QStash

client = QStash("<QSTASH_TOKEN>")
client.queue.get("my-queue")
```
</CodeGroup>