How Personalization and Cache work, in a few words

• Out of the box with 5.3: cache is bypassed for pages with variants. (we removed the contention issues that can occur when doing header negotiation).
  
  • When installing the Personalization module, your cache configuration will be automatically adapted (if it is using the default cache policy) to use a new CachePolicy and Store CacheExecutor, which simply result in bypassing the cache for pages which have variants or are personalized. (info.magnolia.personalization.cache.BypassUncacheableEntriesPolicy and info.magnolia.personalization.cache.BypassVariantsCacheStore respectively)
• Possible: customize cache key to include your traits
  
  • We can’t make that work for everyone without a lot of effort (would need to be configurable, magic, or dumbly add all traits), 
  • We don’t believe this is a good solution: it only works if a majority of pages are personalized AND you have a small amount of traits AND those traits have a small amount of possible values. (It would be completely pointless with a “date” trait, and even just 2 traits with 2 possible values would increase the cache size by 4)
• Future: we will implement another caching mechanism which should allow caching pages with variations while maintaining a reasonably sized cache.
  
  • It will require for trait detectors to be executed before the cache filter, which means performance of these detectors will be paramount to this mechanism working properly.
  • Tech details: cache policy will work with an extra indirection. See sequence diagram below.
• Future: we are investigating component-level caching and Edge Side Includes.

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