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  1. Core Server
  2. SERVER-43981

Simple database query is taking over 10 mins even with a suitable index

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    • Type: Icon: Question Question
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: None
    • Component/s: Index Maintenance
    • None

      We have a collection (called childData) with the following indexes:

      m_childDataCollection.CreateIndex(IndexKeys.Ascending(MongoChildData.ItemIdProperty).Ascending(MongoChildData.ChildIdProperty));
m_childDataCollection.CreateIndex(IndexKeys.Ascending(MongoChildData.RedundantTimeProperty));

      This query runs very fast (less than a second) and returns 59631 :

      db.childdata.find(\{ ItemId: ObjectId('596f322ba28f4b1240f1c2e9') }).count()

      This query takes around 15 minutes:

      db.childdata.find(\{ ItemId: ObjectId('596f322ba28f4b1240f1c2e9') }, \{ItemId : 1, ChId : 1}).toArray()

      We are failing to understand why this second query takes so long even though it is using the index?

      Please note that I have also rebuilt these indexes completely. It took over 3 days to do this!

      Thanks
      Ian

        1. countoutput.txt
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        2. error.png
          error.png
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        3. find_with_itemId_ChId.txt
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        4. find_with_itemId_ChId.txt
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        5. screenshot.png
          119 kB

            Assignee:
            daniel.hatcher@mongodb.com Danny Hatcher (Inactive)
            Reporter:
            ihannah@meniscus.co.uk Ian Hannah
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              Created:
              Updated:
              Resolved: