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D12 Cost and Model Routing: Choosing a Model per Stage, Caching, Degradation, and a Budget Circuit Breaker

• When should you degrade instead of retry, and which dimensions can you degrade first?什么情况下该降级而不是重试？如果决定降级，你有哪些维度可以降，怎么排先后？

  Common in ChinaCommon overseasIntermediate#degradation#retry-strategy

  How to reason about it · think before answering

  1. The pivot is the word instead. This tests whether you separate two failure classes: retry addresses bad luck this time, degradation addresses cannot finish under this configuration. Answering retry three times then degrade misses the point.
  2. Give a reusable rule: retry fixes transient, configuration-independent problems such as rate limits, timeouts and server errors. Degradation fixes persistent, constraint-driven ones such as running out of budget, quota or time. Retrying the second class just burns resources faster.
  3. Name the class most people get wrong: a content-safety block should be neither retried nor degraded, it needs a changed input. Conflating the three is the biggest scoring mistake here.
  4. Order degradation dimensions by how noticeable they are, least to most: resolution, duration, then count of items. Touch the one that changes the content itself only as a last resort.
  5. Add an engineering rule: validate every degradation step against the cost model. If a step saves nothing on your rate card, degrading quality buys you nothing and should be skipped.
  6. Expect the follow-up: when do you decide? Project the cost with a pure function before the run starts and degrade up front. Cutting mid-run leaves a half-finished artifact and wastes everything already spent.

  分析过程 · 先想清楚再作答

  1. 题眼在「而不是」三个字。它考的是你能不能区分两类失败：重试针对的是「这次不巧」，降级针对的是「按当前配置根本跑不完」。答成「先重试三次再降级」就落进了套路。
  2. 给一条可复用的判据：重试解决的是**瞬时**且**与配置无关**的问题（限流、超时、服务端 5xx），降级解决的是**持续**且**由约束导致**的问题（预算不够、配额见底、截止时间快到了）。前者重试有效，后者重试只会把资源烧得更快。
  3. 顺带点出最容易被答错的一类：内容安全拦截既不该重试也不该降级，它要改输入。把三类混在一起是这题最大的失分点。
  4. 降级的维度要按「用户察觉难度」排，从低到高：清晰度、时长、数量（镜头数 / 条数）。先降察觉不到的，最后才动会影响内容本身的那一档。
  5. 还有一条工程判据：每一步降级都要拿成本模型验证一遍。如果某一档在你的单价表上省不出钱（比如更低的清晰度和当前档同价），那这一步降了只有损失，应该直接跳过。
  6. 可预期的追问是「降级要在什么时候决定」。答案是开跑之前先用纯函数预估一遍，算不过就降完再跑——跑到一半再砍，会留下半成品，前面花的钱全打水漂。

  Key points

  • Retry transient configuration-independent failures; degrade when the constraint makes completion impossible
  • Content-safety blocks are a third class: change the input rather than retrying or degrading
  • Order degradation by noticeability: resolution, duration, item count, content last
  • Validate each degradation step against the rate card and skip steps that save nothing
  • Decide before the run starts; cutting mid-run leaves a half-finished artifact and wastes prior spend

  答题要点

  • 重试针对瞬时且与配置无关的失败，降级针对持续且由约束导致的不可完成
  • 内容安全拦截是第三类：既不重试也不降级，要改输入
  • 降级维度按察觉难度排：清晰度、时长、数量，最后才动内容本身
  • 每一步降级都要拿成本模型验证，省不出钱的那一步直接跳过
  • 降级要在开跑前决定，跑到一半再砍会留下半成品且前面的钱白花