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  1. Core Server
  2. SERVER-68006

Investigate plan changes due to changes in heuristic estimation

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Details

    • Task
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • None
    • 6.1.0-rc0
    • None
    • None
    • Fully Compatible
    • QO 2022-08-08, QO 2022-08-22

    Description

      The implementation of a more detailed heuristic CE in SERVER-67166 result in different cardinality estimates than before this task. As a result several plans change. On two occasions the changed plans cause an assertion which is most likely an optimizer bug.

      This bug should investigate the following plan changes in src/mongo/db/query/optimizer/physical_rewriter_optimizer_test.cpp:

      • FilterIndexing4 - changes from covering to non-covering plan with heuristic CE - why?
      • FilterIndexingVariable - same
      • IndexResidualReq2 - the Filter node is moved to just before the Seek. Why? Is this still testing the same functionality?
      • IndexPartitioning, IndexPartitioning1 - results in an failed assert when cardinality estimates change. The assert is in physical_rewriter.cpp: "Must optimize successfully if found compatible properties!"
      • IndexPartitioning1: The interesting thing is that it doesn't fail on each test run, but sometimes, which makes one think the failure depends on rounding errors of cost/cardinality estimates, which in turn results in different sub-plans.

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            svilen.mihaylov@mongodb.com Svilen Mihaylov
            timour.katchaounov@mongodb.com Timour Katchaounov
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              Updated:
              Resolved: