Cache penetration
General caching system, it is in accordance with the key to cache query, if the corresponding value does not exist, they should go to find the back-end systems (such as DB). Some deliberately malicious request query key is not present, a large amount of the request, it will cause a lot of pressure on the back-end systems. This is called caching penetration.
How to avoid?
1: the case where an empty result set also caching and set shorter, or the data key corresponding to the dirty cache after the insert.
2: is not present on certain key filtered. We can put all the possible key into a large Bitmap by the bitmap filter query.
Cache avalanche
When the cache server reboot or a large number of cache concentrated in one time period fail, so that when failure, back-end systems will bring a lot of pressure. Cause the system to crash.
How to avoid?
1: After a cache miss, by locking to control the number of threads or queue database read write cache. For example, a key for allowing only one thread to query the data and write cache, other threads wait.
2: Make secondary cache, cache the original A1, A2 copy is cached, when A1 fails, access to A2, A1 cache expiration time is set short-term, A2 is set for long-term
3: a different key, to set different expiry time for the point in time of a cache miss as uniform as possible
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