What is a nosql database? What's the difference between nosql and rdbms?

1 Understand the difference between acid and alkali (acid is the four requirements for strong consistency of relational database, while alkali is the weak requirement principle for usability and consistency of NoSQL database, which means acid: atomicity, consistency, isolation and persistence; Basic: basically usable, soft, and finally consistent. At the same time, interestingly, in English, acid means acid and alkali means alkali.

Understand the difference between persistence and non-persistence. This is because some NoSQL systems are stored in pure memory.

You must realize the essential difference in data structure between traditional relational database and NoSQL system. Traditional relational databases are usually stored in tables based on rows, while NoSQL systems include column storage (Cassandra), key/value storage (Memcached), document storage (CouchDB) and graph structure storage (Secondary).

4 Unlike the traditional relational database, which has a unified SQL language interface, NoSQL system usually has its own unique API interface.

5. In terms of architecture, you must make it clear that NoSQL system is designed for clusters of hundreds of machines, not the architecture of * * * exclusive database system.

6 in NoSQL system, you may have to get used to not knowing where your data actually exists.

In NoSQL system, you'd better get used to its weak consistency. "final consistency" is an important content in the basic principles. For example, on Twitter, you often feel the delay of data in the list of followers.

In NoSQL system, you must understand that data is not always available.

You have to understand that some schemes have zoning tolerance, while others may not.