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  1. Core Server
  2. SERVER-70395

Slot-Based Engine too aggressively uses disk for $group and is slow

    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Critical - P2 Critical - P2
    • 6.3.0-rc0, 6.0.5
    • Affects Version/s: None
    • Component/s: None
    • Labels:
    • Fully Compatible
    • ALL
    • v6.2, v6.0
    • QE 2023-02-06
    • 10

      Please refer to the discussion here: https://www.mongodb.com/community/forums/t/addtoset-slower-hanging-on-large-collections-since-mongodb-6/192395/3

      In short, there appear to be two issues with the SBE:

      1. It too aggressively resorts to disk for $group processing. In my example above, disk isn't used with the classic engine on 6.0, or on 4.0.
      2. When resorting to disk, it is incredibly slow.

      The only solution was to force the use of the classic query engine, which doesn't seem like a desirable approach.

            david.storch@mongodb.com David Storch
            micallst@gmail.com Steve Micallef
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