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Two member variables of UserInstance class are used to maintain this cache implementation (a home grown cache implementation).
1- systemCache (see UP-1145)
2- systemCharacterCache
If caching is enabled and character caching is NOT enabled then the SAX that represents the user's layout for the folder (tab) they are requesting will be attempted to be cached in the systemCache. If character caching is enabled, the serialized form of that layout will be stored in systemCharacterCache. Both indexed by the cacheKey from constructCacheKey(), which incidentally, has a bad side effect. If you look in processUserLayoutParameters() it manually binds the username to the theme preferences. This guarantees that no two users can share any cache entries. If the character cache is enabled, the system cache is not used.
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