After discussions with anna.wawrzyniak@mongodb.com and martin.neupauer@mongodb.com, the inadvertent change described below has been deemed to have improved performance but not broken anything. Thus it is a rare case where a random mutation actually improved fitness. Therefore I am converting this ticket from a Bug to a Task and will used it just to disambiguate the method names and add more comments about yielding rules. It will not change any functionality.

The original mutation:

SBE PlanStage UnwindStage::getNext() - sbe/stages/unwind.cpp is currently calling a method, checkForInterrupt(), that checks for interrupts but does NOT yield.

When this call was originally added by SERVER-72004, it DID yield.

The ticket SERVER-81812 renamed checkForInterrupt() to checkForInterruptAndYield() but did not convert the call in UnwindStage::getNext() to the new name, then created a new method with the old name checkForInterrupt() that does NOT yield, inadvertently changing SBE UnwindStage from a yielding to a non-yielding stage.

The ticket SERVER-72258 "Audit and add missing checkForInterrupt to SBE stages," added several checkForInterruptAndYield() calls to other stages but did not change UnwindStage.

UnwindStage is used by SBE $lookup, which IS enabled externally. ($unwind itself is not enabled externally in SBE, but the same code is used internally by $lookup.)

FYI martin.neupauer@mongodb.com anna.wawrzyniak@mongodb.com yoonsoo.kim parker.felix@mongodb.com schwerin@mongodb.com matt.broadstone@mongodb.com