An audit of every cache key, asking one question each: if this disappeared, could it be regenerated?
41 key patterns, categorised:
34 derived from the database. safe to lose.
4 expensive to regenerate but possible — a report
that takes 40 seconds. safe, slowly.
3 NOT DERIVABLE. user interface preferences,
written by the browser, read by nothing else,
and living only in the cache.
the three had been there since 2021.A cache that holds the only copy of something is a database with an eviction policy, and the discovery mechanism is a flush — ours came during an unplanned restart. The audit is a spreadsheet and an afternoon, and the useful output is not the list but the rule that came from it: a key is registered with what writes it and what regenerates it, or it does not go in.