Design a system that can convert URLs provided by users into short URLs, allowing users to access their original long URLs using these short URLs. The operation of the system should include, but not be limited to, the following questions: How to allocate short URLs? How to store the mapping between short URLs and long URLs? How to implement the redirection service? How to store access data?

Failover: Failover is a backup operational mode used to enhance system stability and availability. When the primary component fails or is scheduled for downtime, the functions of system components (such as processors, servers, networks, or databases) are transferred to secondary system components.

To improve availability with failover, there are serval ways to achieve the goal such as cold standby, hot standby, warm standby, checkpointing and all active.

If you are asked to design a system to take user-provided URLs and transform them to shortened URLs, what would you do? How would you allocate the shorthand URLs? How would you implement the redirect servers? How would you store the click stats?

Lambda architecture = CQRS (batch layer + serving layer) + speed layer. It solves accuracy, latency, throughput problems of big data.

Using Lambda can address three issues brought by big data: accuracy (good); latency (fast); throughput (high). The lambda architecture can guide us on how to scale a data system.

Nonviolent Communication is not about appearing friendly, nor is it about getting others to do what we want; it concerns mutual understanding between people. There are two ways to strengthen connections and understanding between individuals: expressing our feelings and needs vulnerably; and actively listening to the feelings and needs of others.

KYC is not easy; employees outside the marketing department may never have the opportunity to understand buyers' needs. Buyer persona = buyer profile (who will buy) + buyer insights (when/how/why they buy)

The relational database is the default choice for most storage use cases, by reason of atomicity, consistency, isolation, and durability. How is consistency here different from the one in CAP theorem? Why do we need 3NF and DB proxy?

When customers evaluate a product or service, they weigh perceived value against actual price. The elements of value include functional value; emotional value; life-changing; and social impact.