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  1. Core Server
  2. SERVER-44258

Pipeline optimization does not split a $match with an $or with a single child

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    Details

    • Type: Improvement
    • Status: Open
    • Priority: Major - P3
    • Resolution: Unresolved
    • Affects Version/s: None
    • Fix Version/s: Backlog
    • Component/s: None
    • Labels:
    • Sprint:
      Query 2019-12-16, Query 2019-12-30
    • Linked BF Score:
      24

      Description

      As part of SERVER-36723, a second call to optimizePipeline() was removed as the original intent for doing this was only to absorb a $limit which is no longer necessary. However this introduced a more subtle behavior change, since our pipeline optimization code first attempts to re-order/split stages and then optimizes each individual stage. In the case where a $match has a $or with one child, the second phase will remove the $or altogether. There's a chance that the new $match without the $or can be split and moved ahead of a prior stage, which coincidentally will happen on the second call to optimizePipeline().

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              • Created:
                Updated: