Apache Hama consists of three major components:
It is very similar with Hadoop architecture, only except the portion of communication and synchronization mechanisms.
In a normal usecase the user submits a so called "Job" which is a definition of how to run a computation. A job once submitted will have multiple tasks that are launched across the cluster.
BSPMaster is responsible for the following:
- Maintaining groom server status.
- Maintaining supersteps and other counters in a cluster.
- Maintaining job progress information.
- Scheduling Jobs and assigning tasks to groom servers
- Distributing execution classes and configuration across groom servers.
- Providing users with the cluster control interface (web and console based).
A BSP Master and multiple grooms are started by the script. Then, the bsp master starts up with a RPC server for groom servers. Groom servers starts up with a BSPPeer instance - later, BSPPeer needs to be integrated with GroomServer - and a RPC proxy to contact the bsp master. After started, each groom periodically sends a heartbeat message that encloses its groom server status, including maximum task capacity, unused memory, and so on.
Each time the bsp master receives a heartbeat message, it brings up-to-date groom server status - the bsp master makes use of groom servers' status in order to effectively assign tasks to idle groom servers - and returns a heartbeat response that contains assigned tasks and others actions that a groom server has to do. For now, we have a FIFO job scheduler and very simple task assignment algorithms.
A Groom Server (shortly referred to as groom) is a process that launches bsp tasks assigned by BSPMaster. Each groom contacts the BSPMaster, and it takes assigned tasks and reports its status by means of periodical piggybacks with BSPMaster. Each groom is designed to run with HDFS or other distributed storages. Basically, a groom server and a data node should be run on one physical node to get the best performance. (Data-locality)
A Zookeeper is used to manage the efficient barrier synchronization of the BSPPeers. Later, it will also be used for the area of a fault tolerance system.