SERVER-23654 introduced the $facet stage, which combines all outputs of the sub-pipelines into one result document. This is a request to enable some mechanism for returning more than 16MB of results, while still being able to process the same initial result set in multiple ways.

Original Request

I have several similar aggregation operations at the same time, for example

db.cases.aggregate([
   {$match : query},
   {$unwind : "factors"},

   //operation 1 of the above result
   // ...
])

db.cases.aggregate([
   {$match : query},
   {$unwind : "factors"},

   //operation 2 of the above result
   // ...
])

The first two stages of aggregation( $match, $unwind ) are the same, and I think it would be a waste to repeat the duplicate stages. So I am asking if there exists a way to forking the pipeline, so that it can share the result from the first two stages, as follows,

db.cases.aggregation([
   {$match : query},
   {$unwind : "factors"},
   forks : [
      {... operation 1},
      {... operation 2}
   ]
])

http://stackoverflow.com/questions/38047527/fork-the-pipeline-of-aggregation