Cloudant - Fun with Indexing and Querying

So I was trying to resolve an issue for a colleague, who needed to use an $or operator.

He found that his query would take a very long time ( minutes ) and fail to return any results, searching through ~500K documents.

I tested the problem and, eventually, the solution, using my own data set: -

id,givenName,familyName
1,Maggie,Simpson
2,Lisa,Simpson
3,Bart,Simpson
4,Homer,Simpson
5,Fred,Flintstone
6,Wilma,Flintstone
7,Barney,Rubble
8,Betty,Rubble

In Cloudant, each document looks like this: -

{
  "_id": "1",
  "_rev": "1-0152a3e6867ad34da6e882a80f0fbeff",
  "id": "1",
  "givenName": "Maggie",
  "familyName": "Simpson"
}

{
  "_id": "2",
  "_rev": "1-6bbb94301323a3c3f6ff54f1c3c765e5",
  "id": "2",
  "givenName": "Lisa",
  "familyName": "Simpson"
}

etc.

So this was the query I was using: -

{

  "selector": {

     "familyName": "Simpson",

     "givenName": {

        "$or": [

           {

              "givenName": "Maggie"

           },

           {

              "givenName": "Lisa"

           }

        ]

     }

  },

  "fields": [

     "givenName",

     "familyName"

  ],

  "sort": [

     {

        "givenName": "asc"

     }

  ]

}

In my simple brain, this would return documents for Maggie and Lisa, out of the eight in my database.

I'd previously created this index: -

{
   "index": {
      "fields": [
         "givenName"
      ]
   },
   "name": "givenName-json-index",
   "type": "json"
}

When I ran my query, I got nothing back: -

apart from this statistic: 

Thankfully I found a smart person on our Cloudant Slack channel, who told me where I was going wrong: -

So I changed my query: -

{
   "selector": {
      "$or": [
         {
            "givenName": "Maggie"
         },
         {
            "givenName": "Lisa"
         }
      ]
   },
   "fields": [
      "givenName",
      "familyName"
   ],
   "sort": [
      {
         "givenName": "asc"
      }
   ]
}

and now I see data: -

Yay!

This was also very useful: -

Cloudant NoSQL DB  The- $or operator