CheckpointMetadata

The source of the checkpoint.

• "input": The checkpoint was created from an input to invoke/stream/batch.
• "loop": The checkpoint was created from inside the pregel loop.
• "update": The checkpoint was created from a manual state update.
• "fork": The checkpoint was created as a copy of another checkpoint.

The step number of the checkpoint.

-1 for the first "input" checkpoint. 0 for the first "loop" checkpoint. ... for the nth checkpoint afterwards.

The IDs of the parent checkpoints.

Mapping from checkpoint namespace to checkpoint ID.

The ID of the run that created this checkpoint.

Per-channel update count since the last _DeltaSnapshot was written.

Maps channel name → number of supersteps that wrote to this channel since its last snapshot blob. Used by pregel.create_checkpoint to decide when to write the next snapshot (when the count reaches the channel's snapshot_frequency, snapshot fires and the count resets to 0). Absent on threads that don't use delta channels. Version-format independent — works for int, float, and string version schemes.