Oracle Highly Available Metadata Infrastructure (or HAMI) is a compiled, high-performance, shared-nothing, versioned key-value store. It is based on the well-known RAFT distributed state machine. HAMI maintains a full copy of the object store in its DRAM memory when it is running. Updates to the object store create a log of the changes. At regular intervals, a consistent snapshot of the entire object store is serialized to persistent storage. At restart, HAMI rebuilds the object store in memory from the most recent snapshot. Log records generated since the snapshot are then applied to make the in-memory object store current.

A HAMI ensemble is a set of multi-threaded processes each running on a different server. All ensemble members maintain a private, shared-nothing copy of the same object store through a consensus protocol. At any given time, one voting member is the leader and generates a log describing the changes to the object store. All members apply the same log records to their copy of the object store to ensure they all contain the same data. A change is not committed until a quorum of the members have received and persisted the log record for the change. Only committed changes are visible to the clients of the HAMI service.

Review these requirements and guidelines before you proceed with installing and configuring Highly Available Metadata Infrastructure (HAMI).

The complete bundle of HAMI software is available as a zip file, called hamipack-<release>.zip. It is in the $NMS_BASE/dist/hami/ directory of the NMS installation.