Caching

• Caching avoids redoing the same computationally expensive work.

• You can cache requests from the client and the server.

• You can cache requests from the server and the database.

• write-through cache

  • When you write to the database, you write to the cache and the database.

• write-back cache

  • When you write to the database, you only update the cache, and not the database.
  • Eventually, you write to the database to update.

• caches can become stale if they’re not updated frequently.

• But caches are expensive… What are the most important parts of the system?

• When is caching good?

  • Immutable data
  • Infrequent Writes
  • When you don’t care about stale data
  • Strong Invalidation guarantees.

• Eviction Policies:

  • LRU (Least Recently Used)
  • LFU (Least Frequently Used)
  • LIFO (Last In First Out)
  • FIFO (First in First Out)

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