Reading Note – Cache and Downgrade solution for distribution system

Cache

there is a good explanation about multi-level cache

  • (L1) Level 1 Cache(2KB – 64KB) – Instructions are first searched in this cache. L1 cache very small in comparison to others, thus making it faster than the rest.
  • (L2) Level 2 Cache(256KB – 512KB) – If the instructions are not present in the L1 cache then it looks in the L2 cache, which is a slightly larger pool of cache, thus accompanied by some latency.
  • (L3) Level 3 Cache (1MB -8MB) – With each cache miss, it proceeds to the next level cache. This is the largest among the all the cache, even though it is slower, it’s still faster than the RAM.

Downgrade solution for distribution system

Concept

In order to make sure the main service is still available during extreme situations such as high pressure, server error, or breaking workflow, we can design the downgrade service. The downgrade service will only provide limited services.

The server can automatically downgrade the service regarding key variables. We can also implement a manual solution to switch on/off downgrade service.

Some services can not be downgraded.

Category

  • automatically or manually
  • read service or write service
  • multiple level or single level

Scenario

  • normal: service is not stable because of upgrade and internet. Use automatical solution
  • warning: the stability range from 95% to 100%。 Use automatical solution or manual solution
  • error: availability less than 90%. It may be caused by DB connection pool is full or request is too large. Use automatical solution or manual solution
  • serious error: manual solution

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