Cache Server,

Cache Server,
I. Introduction to cache servers

NoSQL (NoSQL = Not Only SQL), meaning "Not just SQL", refers to non-relational databases. With the rise of Internet Web websites, traditional relational databases are dealing with Web websites, in particular, the ultra-large scale and high-concurrency SNS type web2.0 pure dynamic websites have been unable to cope, exposing many insurmountable problems, non-relational databases have developed rapidly due to their own characteristics. The emergence of NoSQL databases is to solve the challenges posed by multiple data types in large-scale data sets, especially the big data application problems.

Ii. Four major categories of NoSQL database 2.1 key-value storage database

This type of database mainly uses a hash table, which has a specific key and a pointer pointing to specific data. The Key/value model has the advantages of being simple and easy to deploy for IT systems. However, if DBA only queries or updates the part score, the Key/value becomes inefficient. [3] example: Tokyo Cabinet/Tyrant, Redis, Voldemort, Oracle BDB.

2.2-column storage database

These databases are usually used to deal with the massive data stored in distributed storage. Keys still exist, but they point to multiple columns. These columns are arranged by the column family. Example: Cassandra, HBase, Riak.

2.3 Document Database

Document databases are inspired by Lotus Notes office software and are similar to the first type of key-value storage. This type of data model is a version-based document. semi-structured documents are stored in a specific format, such as JSON. Document-based databases can be seen as upgraded versions of key-value databases, allowing nesting of key values between them. Furthermore, document databases are more efficient than key-value databases in queries. For example, CouchDB and MongoDb. There is also a file-type database SequoiaDB in China, which is already open-source.

2.4 different from SQL databases with other columns and rigid structures, Graph databases use flexible Graph models and can be expanded to multiple servers. NoSQL databases do not have a standard query language (SQL), so data models need to be developed for database queries. Many NoSQL databases have restful data interfaces or query APIs. [2] For example, Neo4J, InfoGrid, and Infinite Graph. therefore, we conclude that NoSQL databases are applicable in the following situations: 1. Simple data models; 2. IT systems with higher flexibility; 3. High database performance requirements; 4. High Data Consistency is not required. 5. For a given key, it is easier to map an environment with complex values. Iii. Analysis of four types of NoSQL Databases

　　

Category	Examples example	Typical application scenarios	Data Model	Advantages	Disadvantages
Key-value [3]	Tokyo Cabinet/Tyrant, Redis, Voldemort, Oracle BDB	Content caching is mainly used to process high access loads of a large amount of data, and also for some log systems. [3]	Key-Value pairs that point to Value, which are usually implemented using hash table [3]	Fast search	The data is unstructured and is generally treated as a string or binary data. [3]
Column store database [3]	Cassandra, HBase, Riak	Distributed File System	Stores data in a column cluster and stores data in the same column.	Fast search speed, high scalability, and easy distributed Expansion	Relatively limited functions
Document Database [3]	CouchDB, MongoDb	Web applications (similar to Key-Value, Value is structured, and the difference is that the database can understand the Value content)	Key-Value pairs corresponding to Key-Value. Value is structured data.	The data structure requirements are not strict, the table structure is variable, and the table structure does not need to be pre-defined like a relational database.	The query performance is not high and there is a lack of unified query syntax.
Graph database [3]	Neo4J, InfoGrid, Infinite Graph	Social networks, recommendation systems, etc. Focus on building relationship Graphs	Graph Structure	Graph structure algorithms are used. Such as Shortest Path addressing and N-degree link Lookup	Most of the time, you need to calculate the entire graph to obtain the required information, and this structure is not good for Distributed cluster solutions. [3]