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  1. Compass
  2. COMPASS-6496

Incorrect calculation of "Actual query execution time" for explain plan of aggregation



    • Icon: Bug Bug
    • Resolution: Fixed
    • Icon: Major - P3 Major - P3
    • 1.38.0
    • None
    • Explain
    • None
    • Compass 1.35.0, Mac
    • 3
    • Not Needed
    • Iteration Whale, Iteration Xantic Sargo


      Problem Statement/Rationale

      What is going wrong? What action would you like the Engineering team to take?

      Please be sure to attach relevant logs with any sensitive data redacted.
      Incorrect calculation of "Actual query execution time" for explain plan of aggregation

      Steps to Reproduce

      How could an engineer replicate the issue you’re reporting?

      Connect Compass to an unsharded MongoDB 6.0.4 replica set (this bug may also be reproducible on older versions, or sharded sets but I have not attempted this).

      Create an aggregation from a collection that executes with a cursor in the first stage, and lookup stages that are resolved using 'explainVersion: 2' (slot based execution)
      - Ideally a long-running aggregation pipeline with multiple stages to accentuate the bug

      Click "Explain" and wait for the "Explain Plan" modal to resolve.

      Expected Results

      What do you expect to happen?

      Accurate "Actual query execution time" to be displayed

      Actual Results

      What do you observe is happening?

      Actual query execution time appears to be inflated as the sum of

      + ... stages.[1...n].executionTimeMillisEstimate

      It appears that the stages.0.$cursor.executionStats.executionTimeMillis value is infact the total execution time of the aggregation for all stages

      The values for stages.[1...n].executionTimeMillisEstimate appear to be cumulative running totals (so should not be summed in any case?)

      Additional Notes

      Any additional information that may be useful to include.

      This calculation appears to happen here: https://github.com/mongodb-js/compass/blob/67beee814b386f1b31e6f72230f655af04a59fa2/packages/explain-plan-helper/src/get-execution-stats.ts#L110-L118




            sergey.petushkov@mongodb.com Sergey Petushkov
            ryan@suvera.co.uk Ryan Peggs
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