# Tasks and asynchronous operations
Source: https://www.meilisearch.com/docs/learn/async/asynchronous_operations

Meilisearch uses a task queue to handle asynchronous operations. This in-depth guide explains tasks, their uses, and how to manage them using Meilisearch's API.

Many operations in Meilisearch are processed **asynchronously**. These API requests are not handled immediately—instead, Meilisearch places them in a queue and processes them in the order they were received.

## Which operations are asynchronous?

Every operation that might take a long time to be processed is handled asynchronously. Processing operations asynchronously allows Meilisearch to handle resource-intensive tasks without impacting search performance.

Currently, these are Meilisearch's asynchronous operations:

* Creating an index
* Updating an index
* Swapping indexes
* Deleting an index
* Updating index settings
* Adding documents to an index
* Updating documents in an index
* Deleting documents from an index
* Canceling a task
* Deleting a task
* Creating a dump
* Creating snapshots

## Understanding tasks

When an API request triggers an asynchronous process, Meilisearch creates a task and places it in a [task queue](#task-queue).

### Task objects

Tasks are objects containing information that allow you to track their progress and troubleshoot problems when things go wrong.

A [task object](/reference/api/tasks#task-object) includes data not present in the original request, such as when the request was enqueued, the type of request, and an error code when the task fails:

```json theme={null}
{
    "uid": 1,
    "indexUid": "movies",
    "status": "enqueued",
    "type": "documentAdditionOrUpdate",
    "canceledBy": null,
    "details": {
        "receivedDocuments": 67493,
        "indexedDocuments": null
    },
    "error": null,
    "duration": null,
    "enqueuedAt": "2021-08-10T14:29:17.000000Z",
    "startedAt": null,
    "finishedAt": null
}
```

For a comprehensive description of each task object field, consult the [task API reference](/reference/api/tasks).

#### Summarized task objects

When you make an API request for an asynchronous operation, Meilisearch returns a [summarized version](/reference/api/tasks#summarized-task-object) of the full `task` object.

```json theme={null}
{
  "taskUid": 0,
  "indexUid": "movies",
  "status": "enqueued",
  "type": "indexCreation",
  "enqueuedAt": "2021-08-11T09:25:53.000000Z"
}
```

Use the summarized task's `taskUid` to [track the progress of a task](/reference/api/tasks#get-one-task).

#### Task `status`

Tasks always contain a field indicating the task's current `status`. This field has one of the following possible values:

* **`enqueued`**: the task has been received and will be processed soon
* **`processing`**: the task is being processed
* **`succeeded`**: the task has been successfully processed
* **`failed`**: a failure occurred when processing the task. No changes were made to the database
* **`canceled`**: the task was canceled

`succeeded`, `failed`, and `canceled` tasks are finished tasks. Meilisearch keeps them in the task database but has finished processing these tasks. It is possible to [configure a webhook](/reference/api/webhooks) to notify external services when a task is finished.

`enqueued` and `processing` tasks are unfinished tasks. Meilisearch is either processing them or will do so in the future.

#### Global tasks

Some task types are not associated with a particular index but apply to the entire instance. These tasks are called global tasks. Global tasks always display `null` for the `indexUid` field.

Meilisearch considers the following task types as global:

* [`dumpCreation`](/reference/api/tasks#dumpcreation)
* [`taskCancelation`](/reference/api/tasks#taskcancelation)
* [`taskDeletion`](/reference/api/tasks#taskdeletion)
* [`indexSwap`](/reference/api/tasks#indexswap)
* [`snapshotCreation`](/reference/api/tasks#snapshotcreation)

<Note>
  In a protected instance, your API key must have access to all indexes (`"indexes": [*]`) to view global tasks.
</Note>

### Task queue

After creating a task, Meilisearch places it in a queue. Enqueued tasks are processed one at a time, following the order in which they were requested.

<Warning>
  When the task queue reaches its limit (about 10GiB), it will throw a `no_space_left_on_device` error. Users will need to delete tasks using the [delete tasks endpoint](/reference/api/tasks#delete-tasks) to continue write operations.
</Warning>

#### Task queue priority

Meilisearch considers certain tasks high-priority and always places them at the front of the queue.

The following types of tasks are always processed as soon as possible in this order:

1. `taskCancelation`
2. `upgradeDatabase`
3. `taskDeletion`
4. `indexCompaction`
5. `export`
6. `snapshotCreation`
7. `dumpCreation`

All other tasks are processed in the order they were enqueued.

## Task workflow

When you make a [request for an asynchronous operation](#which-operations-are-asynchronous), Meilisearch processes all tasks following the same steps:

1. Meilisearch creates a task, puts it in the task queue, and returns a [summarized `task` object](/learn/async/asynchronous_operations#summarized-task-objects). Task `status` set to `enqueued`
2. When your task reaches the front of the queue, Meilisearch begins working on it. Task `status` set to `processing`
3. Meilisearch finishes the task. Status set to `succeeded` if task was successfully processed, or `failed` if there was an error

<Note>
  **Terminating a Meilisearch instance in the middle of an asynchronous operation is completely safe** and will never adversely affect the database.
</Note>

### Task batches

Meilisearch processes tasks in batches, grouping tasks for the best possible performance. In most cases, batching should be transparent and have no impact on the overall task workflow. Use [the `/batches` route](/reference/api/batches) to obtain more information on batches and how they are processing your tasks.

### Canceling tasks

You can cancel a task while it is `enqueued` or `processing` by using [the cancel tasks endpoint](/reference/api/tasks#cancel-tasks). Doing so changes a task's `status` to `canceled`.

<Note>
  Tasks are not canceled when you terminate a Meilisearch instance. Meilisearch discards all progress made on `processing` tasks and resets them to `enqueued`. Task handling proceeds as normal once the instance is relaunched.
</Note>

### Deleting tasks

[Finished tasks](#task-status) remain visible in [the task list](/reference/api/tasks#get-tasks). To delete them manually, use the [delete tasks route](/reference/api/tasks#delete-tasks).

Meilisearch stores up to 1M tasks in the task database. If enqueuing a new task would exceed this limit, Meilisearch automatically tries to delete the oldest 100K finished tasks. If there are no finished tasks in the database, Meilisearch does not delete anything and enqueues the new task as usual.

#### Examples

Suppose you add a new document to your instance using the [add documents endpoint](/reference/api/documents#add-or-replace-documents) and receive a `taskUid` in response.

When you query the [get task endpoint](/reference/api/tasks#get-one-task) using this value, you see that it has been `enqueued`:

```json theme={null}
{
    "uid": 1,
    "indexUid": "movies",
    "status": "enqueued",
    "type": "documentAdditionOrUpdate",
    "canceledBy": null,
    "details": {
        "receivedDocuments": 67493,
        "indexedDocuments": null
    },
    "error": null,
    "duration": null,
    "enqueuedAt": "2021-08-10T14:29:17.000000Z",
    "startedAt": null,
    "finishedAt": null
}
```

Later, you check the task's progress one more time. It was successfully processed and its `status` changed to `succeeded`:

```json theme={null}
{
    "uid": 1,
    "indexUid": "movies",
    "status": "succeeded",
    "type": "documentAdditionOrUpdate",
    "canceledBy": null,
    "details": {
            "receivedDocuments": 67493,
            "indexedDocuments": 67493
    },
    "error": null,
    "duration": "PT1S",
    "enqueuedAt": "2021-08-10T14:29:17.000000Z",
    "startedAt": "2021-08-10T14:29:18.000000Z",
    "finishedAt": "2021-08-10T14:29:19.000000Z"
}
```

Had the task failed, the response would have included a detailed `error` object:

```json theme={null}
{
    "uid": 1,
    "indexUid": "movies",
    "status": "failed",
    "type": "documentAdditionOrUpdate",
    "canceledBy": null,
    "details": {
            "receivedDocuments": 67493,
            "indexedDocuments": 0
    },
    "error": {
        "message": "Document does not have a `:primaryKey` attribute: `:documentRepresentation`.",
        "code": "internal",
        "type": "missing_document_id",
        "link": "https://docs.meilisearch.com/errors#missing-document-id"
    },
    "duration": "PT1S",
    "enqueuedAt": "2021-08-10T14:29:17.000000Z",
    "startedAt": "2021-08-10T14:29:18.000000Z",
    "finishedAt": "2021-08-10T14:29:19.000000Z"
}
```

If the task had been [canceled](/reference/api/tasks#cancel-tasks) while it was `enqueued` or `processing`, it would have the `canceled` status and a non-`null` value for the `canceledBy` field.

After a task has been [deleted](/reference/api/tasks#delete-tasks), trying to access it returns a [`task_not_found`](/reference/errors/error_codes#task_not_found) error.