跳槽学习打卡

Day 1, Machine learning yearning 55 pages, Head first design patterns Chapter 1

Day 5, how to make your web service scalable?
Clone: load balancer + multiple servers with the same code base + centralized session database (cache).
database: 1. mysql, master-slave replication (read from slaves, write to master), upgrade your master server by adding RAM 2. denormalize, NOSQL, dataset join is slow and so cache is needed
cache: query as key or object as key (did not get it well), Memcached or Redis
Asynchronism: 1, pre-rendered and locally stored 2. a queue of tasks or jobs that a worker can process (like RabbitMQ)

Day 6, Java concepts:
Arrays.sort(), Collections.sort(), comparable object (override compareTo), pass comparator (override compare)
Overload(can not overload by return type), Override
Static (belongs to class instead of object), serialization (persistent, implements Serializable) <-> Transient (variable should not be serialized), Volatile (being stored in main memory, fix visibility issues but sill have race condition)

Day 4,Design pattern.
Singleton Pattern (eg: logging, lazy loading, thread safe),
Factory Pattern (The factory instantiates a new concrete product),
Observer Pattern (eg: MVC, Publish-subscribe, push-pull, observable subject, observer),
Decorator Pattern (vs inheritance, wrap one object with another object, makes run-time object changes easier)

Day 2, Union-Find [输入是边的问题，online algorithm], Map Reduce Design, Machine learning yearning 55 - 71 pages

Day 3, 粗略看了一下 LBS 的大致deisgn， 对不同类型的NoSQL和geohash 不是很懂，明天接着看

Day 7, Geohash encode & decode

Day 8, Design Twitter, learn User systems & database. a service -> a database -> a data structure.

Day 9, array based DP

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