Refactor cost model by splitting up the various steps into defined tiebreakers#3993
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alecgrieser wants to merge 18 commits intoFoundationDB:mainfrom
Open
Refactor cost model by splitting up the various steps into defined tiebreakers#3993alecgrieser wants to merge 18 commits intoFoundationDB:mainfrom
alecgrieser wants to merge 18 commits intoFoundationDB:mainfrom
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… interface definition
One thing that was subtle was that the choice of PickLeft (always returning -1) meant that the comparison in the PlanGenerator was always updating to the new plans when one was available. This flips the comparison so that we now only update the plan if the new plan is strictly better than the old plan. Because the as-yet-best plan is the right operand in the comparator, ties will result in us sticking with that plan.
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… few teamscale things
… as the stable selector cost model
…f RewritingCostModel
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This is some refactoring work on the
CascadesCostModels to allow the re-use of the various conditions that go into it. It breaks up the work into definedTiebreakersteps, each of which does one comparison that can return either a negative number, a positive number, or zero, just like aComparator. The cost models have then been modified so that they string those steps along, invoking each tie breaker in turn until it gets a non-zero one.This comes from a larger branch of work from @normen662 that also does some pre-pruning along the way with a smaller set of these
Tiebreakers. This work is a preliminary step to that, and as such, it does not aim to modify any behavior, instead just reorganizing the existing logic.