Solving problems with cache
We spent a lot of time on providing good caching, that is, saving intermediate results and serving saved copies instead of recalculating from scratch for the same requests. This works perfectly only in a perfect world (for example, a pure functional world where functions and, by extension, GET/HEAD HTTP requests do not have side effects). In the real world, two equal requests may sometimes lead to different responses. There are two basic reasons for it: the earlier-mentioned side effects, which change the state despite the perceived idempotence of GET/HEAD, or flawed equality relationship between requests. A good example of this is ignoring wall time when the response depends on it.
Such problems usually manifest themselves ...
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