When comparing MySQL vs CouchDB, the Slant community recommends CouchDB for most people. In the question“What are the best databases to use for Node.js applications?” CouchDB is ranked 3rd while MySQL is ranked 6th. The most important reason people chose CouchDB is:
CouchDB works very well even when the network is physically partitioned
Specs
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Pros
Pro Scalable
MySQL is made to handle a lot of data and to be used in large applications. This makes it extremely scalable and fast, even under a lot of workload.
Pro Multiple third-party tools that help working with MySQL
Since MySQL is one of the most popular relational databases, maybe the most popular, there exist many third-party tools and applications that help developers to use MySQL in their development.
Pro Easy to start working with
Because of it's popularity there are a lot of tutorials and guides out there that help developers install and work with MySQL. The installation process itself is not very hard and there are multiple powerful GUI tools that make it extremely easy to work with MySQL for a beginner.
Pro Works well between physical network partitions
CouchDB works very well even when the network is physically partitioned
Pro Available
CouchDB is considered an available DMS according to the ACP theory of database management. As such it allows every client to always read and write
Pro Useful for applications where versioning is important
CouchDB is mostly used in applications where a large amount of data needs to be accumulated and where data only changes rarely.
Pro Changes API
You can use the RESTful API to listen for changes in your database, which is something most databases can't do. It makes it really easy for clients to keep their view of data up-to-date.
Pro RESTful API
Since everything is stored as a JSON document and served over HTTP, it's perfectly suited for communicating with client-side javascript, with or without middleware.
Cons
Con Error messages usually are not very detailed
When you are trying to do something in MySQL and something goes wrong it will simply give you an error message with an error code. Which does not say much about what went wrong unless you look it up online. This can be a little cumbersome during development.
Con Can only achieve consistency through replication and verification
Since CouchDB is considered an AP (Available, Partition-Tolerant database management system), it is not really consistent (not all clients can have the same view of the data consistently) and the only way to achieve some "eventual consistency" is through replication and verification of data.
Con Uncertain future
After a very promising start, development began to drag after major supporters like Canonical, Selenium and CouchOne either shut down or moved to other tools. Development has begun to pick up again.