pekko: show bucket a shed by the endpoint total - #1967
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A request has to pass the bucket limiter and the endpoint total. The bucket is tried first, so when the total is what refuses the request the bucket has already admitted it and the permits are handed back. That release was indistinguishable from a completed request, which disabled both halves of the fair-share policy for the shed caller: it accrued no demerit, so it never became a hog however hard it hammered, and it was never counted as wanting capacity, so the other callers kept a cap of the whole budget and could borrow all of it while it waited. Any endpoint whose dedicated buckets consume enough of the total for it to bind first had fair sharing in name only. Add `releaseDenied` to ConcurrencyLimiter, defaulting to a plain release since a limiter that keeps no per-caller state cannot care, and have the endpoint use it for the rollback. FairShareLimiter records the caller as having attempted and been refused, exactly as if the bucket had refused it directly. A shed that hands back nothing records nothing, which keeps a mis-paired call the no-op that `release` already is.
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A request has to pass the bucket limiter and the endpoint total. The bucket is tried first, so when the total is what refuses the request the bucket has already admitted it and the permits are handed back. That release was indistinguishable from a completed request, which disabled both halves of the fair-share policy for the shed caller: it accrued no demerit, so it never became a hog however hard it hammered, and it was never counted as wanting capacity, so the other callers kept a cap of the whole budget and could borrow all of it while it waited. Any endpoint whose dedicated buckets consume enough of the total for it to bind first had fair sharing in name only.
Add
releaseDeniedto ConcurrencyLimiter, defaulting to a plain release since a limiter that keeps no per-caller state cannot care, and have the endpoint use it for the rollback. FairShareLimiter records the caller as having attempted and been refused, exactly as if the bucket had refused it directly.A shed that hands back nothing records nothing, which keeps a mis-paired call the no-op that
releasealready is.