Sort using nested_filter internal implementation and performance concerns

Elastic Stack Elasticsearch
1

The description for nested_filter is:

"Common case is to repeat the query / filter inside the nested filter or
query. "

If my search involves something like:

GET /library/book/_search
{
"query": {
"nested": {
"path": "prices",
"score_mode": "total",

  •  "query": {*

  •    "match": {*

  •      "region": "cities"*
  }
}
    }
    },
    "sort": [
    {
    "price": {
    "mode": "avg",
    "order": "asc",
    "nested_path": "prices",
    "nested_filter": {
  •      "query": {*

  •        "match": {*

  •          "region": "cities"*
      }
    }
  }
}
    },
    "_score"
    ]
    }

If you run a sort on a nested field and use the nested_filter, how is that
implemented internally?

Secondly, are there any performance concerns or gotchas?

In this case, the query is repeated for the hits and for the sort. How much
of a concern is this? What if there were multiple sort fields used and each
sort field has query repeated?

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