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  1. Core Server
  2. SERVER-58426

Add planning logic for $lookup

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    • Icon: Task Task
    • Resolution: Fixed
    • Icon: Major - P3 Major - P3
    • 5.3.0
    • None
    • None
    • None
    • Fully Compatible
    • QE 2022-02-07, QE 2022-02-21

    Description

      We must add logic to the query planner for planning a $lookup. This involves examining the size of the collections involved and choosing the join algorithm (nlj or hashed) using the heuristic we agreed on here:

       

      Foreign collection has index to answer join predicate? Size of foreign collection Strategy
      Yes Anything Indexed NLJ
      No < 10k docs Hash Join (foreign side is build side)
      No >= 10k docs NLJ

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            mihai.andrei@mongodb.com Mihai Andrei
            ian.boros@mongodb.com Ian Boros
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