Order of $sort and $limit aggregation

Working with Data Node.js Frameworks
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3

Just replyig your first half of the post

Not 100% sure, but I believe they are doing it like that to get user input, which could be done different anyways, as a function myPipeline(skip, limit) could retrieve the full pipeline as an aggregation, etc.

But after all that is converted into a single query, and they are seeing the top-k / coalescence sorting, from the pipeline optimization.

Note that sort + limit are normally merged together, and if there is a skip, is between limit and sort, sort will done also using skip+limit.

{ $sort: { age : -1 } },
{ $skip: 10 },
{ $limit: 5 }

{
   "$sort" : {
      "sortKey" : {
         "age" : -1
      },
      "limit" : NumberLong(15)
   }
},
{
   "$skip" : NumberLong(10)
}

With all this said, you may be able to move skip to the first stages such that it occurs before the $lookup…