Covering vs non-covering index

Couchbase Server
1

I have a document type like

{
    "type":"REGISTER",
    "id":"0c7abd73-cbd8-48b4-bb79-808eec83f79c",
    "userId":"d448e08e-5f0e-4b52-aec8-e4d3a487548b",
    "token":"LONG STRING UP TO 10KB"
}

I want to run SELECT token FROM default WHERE userId='d448e08e-5f0e-4b52-aec8-e4d3a487548b'

As token is long string (up to 10KB) , is it recommended I cover index (userId,token) ? Or I must use userId for index?

2

It all depends on avg size and total documents. You should try and see which one performs better.