State Keeper

Runtime Information Stored in the State Keeper

Primary Nodes

Within each copyset, one node is the primary copy, which both stores data and provides read access. Other nodes are secondary nodes that store backup copies of the data. The state keeper records which node is the primary.

Data Distribution Mapping

The state keeper determines the mapping that assigns each table row to a copyset.

State Keeper Fault Tolerance

A set of fault-tolerant state keeper processes protect this crucial information and ensure nonstop access to it. One state keeper process supplies this information to the proxies and copyset nodes.

In production environments, use three processes. In a prototyping or testing environment, only one process suffices.

For added protection, each state keeper process also maintains a copy of the governing decisions in a disk file.