NoSQL contender CouchDB's been dropped by Ubuntu's ambitious cloud synchronisation service.

The Linux distro said it has given up on the open-source CouchDB in Ubuntu One after three years trying and failing to make the document store scale to millions of users and databases.

Canonical's John Rowland Lenton said here: "Our situation is rather unique, and we were unable to resolve some of the issues we came across.

"We were thus unable to make CouchDB scale up to the millions of users and databases we have in our data centres, and furthermore we were unable to make it scale down to be a reasonable load on small client machines."

Lenton said Ubuntu One contacts, notes and play lists databases would continue to run on its servers but that direct external access to the underlying databases will be shut off.

Ubuntu One, introduced in 2010, is the Linux distro's online data and music service.

It gives you up to 20GB of online storage, lets you sync files between different devices and allows you to stream music to iPhone and Android devices.

CouchDB is the Erlang-based document storage system written by former Lotus-Notes developer Damien Katz, which in 2008 became an official project of the Apache Software Foundation (ASF). Katz is CTO of the CouchDB support company Couchbase.

CouchDB is one of a crowed of NoSQL databases that have become popular in recent years because of their use in large-scale web properties including Facebook and Twitter; they promised to overcome the management and speed of data access "shortcomings" of relational database management systems. Such databases are now trying to pick up customers among the regular, enterprise crowd and such is the interest this opportunity has generated that database market leader Oracle has released what it claims is its own NoSQL database.

CouchDB is a document-oriented data storage system whose users include the BBC and parts of Facebook. It competes with NoSQL document store MongoDB. ®