Notes

Caching -
a short term memory to access data at a faster rate.
ways to implement -
1. distributed cache -
cache is distributed across several nodes or machines or servers.
Adv - increased cache space.
disadv - if a node fails then data or cache stored in that node is lost.
2. global cache -
a single machine to store all cache.
useful to store cache of some fixed data.
two ways to implemnt - 1.server-cache-db
2.server-cache & server-db
Most applications leveraging global caches tend to use the first type, where the cache itself manages eviction and fetching data to prevent a flood of requests for the same data from the clients
3. cdn - it is used to implement in sites serving large amount of static data.

Cache invalidation - If the data is modified in the database, it should be invalidated in the cache, if not, this can cause inconsistent application behavior.
schemes for cache invalidation -
1. write through cache - every write operation is done in both cache and database at same time.it minimizes risk of data loss but increase latency of write operation.
2. write around cache - write operation is done in db directly bypassing cache. it prevents cache to be flodded but a read request increase latency.
3. write back cache - data is written to cache alone at the first request. on regular interval of time data is updated into database from cache.it gives low latency and high throughput for write intensive applications.

Data structurs -
LIFO,FIFO,LRU,MRU,LFU,RR