Galaxy

Galaxy is a high-performance in-memory data-grid (IMDG) that can serve as a basis for building distributed applications that require fine-tuned control over data placement and/or custom distributed data-structures. What makes Galaxy different from other IMDGs is the way it assigns data items to cluster node. Instead of sharding the data on one of the keys using a consistent hashing scheme, Galaxy dynamically moves objects from one node to another as needed using a cache-coherence protocol similar to that found in CPUs. This makes Galaxy suitable for applications with predictable data access patterns, i.e. applications where the data items behave according to some proximity metric, and items that are “closer” together are more likely to be accessed together than items that are “far” apart.Galaxy is not a key-value store, though it can be used to build one. It is meant to be used as a low-level platform for building distributed data structures. Galaxy uses ZooKeeper or JGroups for cluster management, and BerkeleyDB or any SQL database for optional persistence. The Galaxy server runs as a standalone process. Regular Galaxy cluster nodes are called “peers”, and to configure a peer, take a look at peer.xml in the config directory. The peers are users’ application code that calls into the Galaxy library. In users’ application code, users need to get an instance of the Grid class , which is the entry point to Galaxy’s API. Note that if users are using ZooKeeper, users must start the ZooKeeper servers before starting any Galaxy nodes. A number of pre-built configurations are included with the Galaxy distribution, and can be found in the config directory.