The fastest answer is also the easiest one to get wrong.
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Caching is the fastest way to make a slow system fast, and also the fastest way to make a correct system wrong. Every cache is a copy of the truth that the truth no longer knows about, and every cache invalidation is a small race against the next read.
Most caching bugs are not bugs in the cache. They are bugs in the team’s mental model of when the cache is allowed to lie.
Cache deliberately. Document the staleness. The cache that nobody can explain is the cache that will eventually embarrass you.
