Checkpoint
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 that node is called the node’s Checkpoint Epoch. It 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 the nodes, known as the Last Good Epoch (LGE).