Hi I'm looking for best practices with API design to batch update a collection with an API call.

My collection has URL /api/v1/cars and I would like to update all the cars in the collection to add a timestamp of the current time.

```
{
    data: [
    {
        manufacturer: 'Porsche',
        timestamp: ...
    },
    {
        manufacturer: 'BMW',
        timestamp: ...
    }
    {
        manufacturer: 'Peugeot',
        timestamp: ...
    }
}

```

I thought about a few options but I can't figure what is the best practice.

Should it be:

1/ Modelled as another resource such as `POST api/v1/cars/updateTimestamp`

2/ Passed as a query parameter: `PUT api/v1/cars?updateTimestamp`

3/ Pass in the body of the request: 

```
POST api/v1/cars 
{"operation":"Update timestamps"}

```

I'd like to emphasize that the whole processing should be done on the back-end and not passed by the client.
Same problem would happen for any complex processing that happens on the back end.. 
How could I keep the API RESTy in this case.

Thanks a lot for your help/any pointer to relevant ressources.