NoSQL Database
中文版：非关系型数据库
A non-relational database designed to store and retrieve semi-structured and unstructured data.
Definition
- NoSQL database is unstructured data.
- It was designed to overcome big data’s scalability and performance issues, which traditional databases were not designed to address.
- It is specifically used when organizations need to access, process, and analyze a large volume of unstructured data.
Four Main Types
| Type | Description | Examples |
|---|---|---|
| Key-Value Store | Simplest NoSQL model; data split into key and value | Amazon DynamoDB, Riak, Redis, Berkeley DB, Memcached, Hamster DB |
| Column-Store | Stores data as columns instead of rows | HBase, Cassandra |
| Document Database | Stores flexible documents in field-value pairs (JSON, XML) | MongoDB, CouchDB, Microsoft DocumentDB |
| Graph Database | Represents data as nodes, edges, and properties | Neo4J, InfiniteGraph, HypherGraphDB, AllegroGraph, GraphBase, OrientDB |
Key-Value Store
- Key-value databases are the simplest of the NoSQL databases.
- The data is usually split into two parts: key and value.
- The key is a string, and the value is the actual data; hence the reference key-value pair.
Column-Store Database
- A column-oriented database stores the data as columns instead of storing them as rows.
- The working method is that it saves data into sections of columns rather than sections of rows.
- Based on data retrieval needs, data can be stored as row-oriented (OLTP) or column-oriented (OLAP).
- The key difference is the way the data are physically stored on disk:
- Row-oriented databases store the whole row in the same block, if possible.
- Columnar databases store columns in subsequent blocks.
Document Database
- A document is a record in a document database.
- Instead of storing data in fixed rows and columns, document databases use flexible documents.
- Documents store data in field-value pairs.
- The values can be a variety of types and structures, including strings, numbers, dates, arrays, or objects.
- Documents can be stored in formats like JSON or XML.
- A group of documents is called collections.
- Collections typically store documents that have similar contents.
Graph Database
- The graph is a pictorial representation of data in the form of nodes and relationships which are represented by edges.
- It has three components: nodes, relationships, and properties.
- Nodes: represent the objects or instances; equivalent to a row in database; act as a vertex in a graph.
- Relationships: represent the edges; have a specific direction, type and form patterns of the data.
- Properties: information associated with the nodes.
Related Concepts
- Relational Database — Structured alternative with ACID guarantees
- OLTP vs OLAP — Row-oriented vs column-oriented storage