CouchDB is often categorized as a “NoSQL” database. While this term is a rather generic characterization of a database, or data store, it does clearly define a break from traditional SQL-based databases. A CouchDB database lacks a schema, or rigid pre-defined data structures such as tables. Data stored in CouchDB is a JSON document(s). The structure of the data, or document(s), can change dynamically to accommodate evolving needs.
What it is Not
To better understand what CouchDB is, it may be helpful to understand a few things that CouchDB isn’t:
- A relational database
- A replacement for all databases.
- An object-oriented database. While CouchDB stores JSON objects, it isn’t meant to function as a seamless persistence layer for an object-oriented programming language.
Let’s review some of the basic elements of CouchDB.
A CouchDB document is a JSON object that consists of named fields. A CouchDB database is a flat collection of these documents. Each document is identified by a unique ID.
Views are the method of aggregating and reporting on the documents in a database, and are built on-demand to aggregate, join and report on database documents. Views are built dynamically and don’t affect the underlying document; you can have as many different view representations of the same data as you like.
CouchDB is designed to store and report on large amounts of semi-structured, document oriented data. CouchDB greatly simplifies the development of document oriented applications.
With CouchDB, no schema is required, so new document types with new meaning can be safely added alongside the old.
CouchDB is a peer based distributed database system. Any number of CouchDB hosts (servers and offline-clients) can have independent “replica copies” of the same database.
CouchDB has built-in conflict detection and management and the replication process is incremental and fast, copying only documents changed since the previous replication, the replication in CouchDB is the result of careful ground-up design, engineering and integration. This replication framework provides a comprehensive set of features:
- Master → Slave replication
- Master ↔ Master replication
- Filtered Replication
- Incremental and bi-directional replication
- Conflict management
Uses case for CouchDB
There are several use cases that are good uses of CouchDB and other NoSQL repositories. A few that come to mind are:
- Synchronizing data in an occasionally connected solution. This makes sense in industries like finance where data manipulation or forecasting is done in a disconnected state and synchronized with a server.
- High velocity log writes
- High performance caching