You can't always put all your relational data in a single relational database. Sometimes you simply have too much data. Sometimes you have a distributed deployment architecture (network latency between California and India might be too high to have a single database). There might even be non-technical reasons (a potential customer simply won't do the deal unless her company's data lives in its own db instance). Whatever your reasons, talking to multiple relational databases inevitably complicates the development of your application. Hibernate Shards is a framework that is designed to encapsulate and minimize this complexity by adding support for horizontal partitioning on top of Hibernate Core. Simply put, we aim to provide a unified view of multiple databases via Hibernate.

So what's a shard? Good question. "Shard" is just another word for "segment" or "partition," but it's the term of choice within Google. Hibernate Shards was originally the 20 percent project of a small team of Google engineers, so the project nomenclature revolved around shards from the beginning. We're open sourcing what we have so far because we want the Hibernate community to be able to benefit from our efforts as soon as possible, but also with the hope and expectation that this community will be able to help us reach a GA release much faster than if we kept this under wraps. We fully expect to find glitches in both our design and implementation, and we appreciate your patience as we work through them.