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  1. Core Server
  2. SERVER-14130

Query planner could consider additional query plans for $or

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    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Duplicate
    • Affects Version/s: 2.6.1
    • Fix Version/s: None
    • Component/s: Querying
    • Labels:
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      Description

      Prior to 2.6, the query planner would consider plans for $or beneath an $and according to a logical rewrite to disjunctive normal form. For example, suppose we have indices {a: 1, b: 1} and {a: 1, c: 1}. For the query

      db.coll.find({a: 3, $or: [{b: 4}, {c: 5}]});

      the query planner would instead plan this as

      db.coll.find({$or: [{a: 3, b: 4}, {a: 3, c: 5}]});

      The first clause uses the index {a: 1, b: 1} and the second uses {a: 1, c: 1}.

      In 2.6, the query planner does not consider this rewrite and therefore can miss some of the plans considered by 2.4.

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              Assignee:
              hari.khalsa@10gen.com hari.khalsa@10gen.com
              Reporter:
              david.storch David Storch
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                Resolved: