Atlas search with conditions and why MUST works faster than SHOULD and followed by other?

MongoDB Atlas Atlas Search
,
8

I have modified the document schema for using data -

{
    "_id" : ObjectId("63cf39df1d7798a846b2eb0e"),
    "articleid" : "9d23e3ab-9b7d-11ed-a650-b0227af59807",
    "headline" : "Microsoft to Put $10b More in ChatGPT Maker OpenAI",
    "subtitle" : "OpenAI needs Microsoft’s funding and cloud-computing power to run increasingly complex models",
    "fulltext" : "\nMS Adds $1()B to Investment in ChatGPT Maker",
    "pubdate" : "2023-01-24",
    "article_type" : "print",
    "date" : ISODate("2023-01-24T00:00:00.000+0000")
}

I am facing 2 Major performance issues.

  1. I have 10 Million records in the collection, in the field - headline, subtitle, fulltext I am trying to find the words with Operator like - must, should, and simple search.

  2. Now Whenever I run a must query it is always faster and return the result within 10 seconds no matter how big the query is, but in the case of a should or a simple search of a single word it takes more than 50 seconds why?

Now, I was thinking due to large data like 10 Million I need to filter data based on date first and then search full text search, in this way I can get result much faster.

Below are my sample queries -

Should -

db.getCollection("article_fulltext").aggregate([
    {
        "$search":{
            "index":"fulltext",
            "compound":{
                "filter":[
                    {
                        "range":{
                            "path":"date",
                            "gte":"ISODate(""2023-01-01T00:00:00.000Z"")",
                            "lte":"ISODate(""2023-01-31T00:00:00.000Z"")"
                        }
                    }
                ],
                "should":[
                    {
                        "text":{
                            "query":"CHATGPT",
                            "path":[
                                "headline",
                                "fulltext",
                                "subtitle"
                            ]
                        }
                    },
                    {
                        "text":{
                            "query":"OPENAI",
                            "path":[
                                "headline",
                                "fulltext",
                                "subtitle"
                            ]
                        }
                    }
                ],"minimumShouldMatch": 1
            }
        }
    }
])

simple search -

db.getCollection("article_fulltext").aggregate([{
    $search:{
        index:"fulltext",
        text:{
            query:"Microsoft",
            path:["headline", "fulltext", "subtitle"]
        }
    }
}])

Atlas search Index -

{
  "mappings": {
    "dynamic": false,
    "fields": {
      "articleid": {
        "type": "string"
      },
      "fulltext": {
        "type": "string"
      },
      "headline": {
        "type": "string"
      },
      "subtitle": {
        "type": "string"
      }
    }
  }
}

I am facing issues with the above queries, as I am getting really good performance with must search!