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  1. Core Server
  2. SERVER-36994

$expr does not use index for $in

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Duplicate
    • 3.6.7, 4.0.2
    • None
    • Aggregation Framework
    • None
    • ALL
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      Create a new collection.

      Create index :

      db.debug.createIndex({ 'item': 1 })

      Insert data :

      db.debug.insert({ item: "card", qty: 15 })
      		 
      db.debug.insert({ item: "table", qty: 15 })
      		 
      db.debug.insert({ item: "piano", qty: 15 })
      		 
      db.debug.insert({ item: "house", qty: 15 })
      		 
      db.debug.insert({ item: "test", qty: 15 })

      Query :

      db.debug.explain().aggregate([{
      		 
      "$match": {"$expr": {"$in": ["$item", ["card", "test"]]}}
      		 
      }])

      Wining Plan

      "winningPlan" : {
      		 
          "stage" : "COLLSCAN", 
          "filter" : {
      		 
              "$expr" : {
      		 
                  "$in" : [
      		 
                      "$item", 
                      {
      		 
                          "$const" : [
      		 
                              "card", 
                              "test"
      		 
                          ]
      		 
                      }
      		 
                  ]
      		 
              }
      		 
          }, 
          "direction" : "forward"
      		 
      },

       

      Show
      Create a new collection. Create index : db.debug.createIndex({ 'item' : 1 }) Insert data : db.debug.insert({ item: "card" , qty: 15 }) db.debug.insert({ item: "table" , qty: 15 }) db.debug.insert({ item: "piano" , qty: 15 }) db.debug.insert({ item: "house" , qty: 15 }) db.debug.insert({ item: "test" , qty: 15 }) Query : db.debug.explain().aggregate([{ "$match" : { "$expr" : { "$in" : [ "$item" , [ "card" , "test" ]]}} }]) Wining Plan "winningPlan" : { "stage" : "COLLSCAN" , "filter" : { "$expr" : { "$in" : [ "$item" , { "$const" : [ "card" , "test" ] } ] } }, "direction" : "forward" },  

    Description

      An $expr expression in a query will not use an index when used with $in.

      The goal was to used it in a $lookup pipeline.

      The problem seems to exists in 3.6.3 as well as 4.0.2

      Attachments

        Issue Links

          duplicates

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-32549 allow $expr with $in expression use a non-multikey index

          • Major - P3 - Major loss of function.
          • Backlog

          Activity

            People

              Unassigned Unassigned
              Mathias Claux Mathias C.
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              Dates

                Created:
                Updated:
                Resolved: