Checkpoint Epoch
Every time the Tuple Mover performs a move-out operation for a given projection, it records a checkpoint epoch for that projection, representing an epoch up to which the projection has no data in the WOS. The minimum checkpoint epoch across all projections on a given node is that node’s checkpoint epoch, which represents a point in time up to which all the data was moved out to disk. If a K-safe=1 database experiences a single-node failure, the node's recovery process attempts to rebuild the data beyond the checkpoint epochs from other nodes. If all nodes fail, such as during a power outage, recovers the database back to the minimum checkpoint epochs across all nodes, or last good epoch (LGE).