ErrInvalidDynamoDBSchema is returned when there are one or more fields missing from the table.

ErrShardClaimed is returned when shard is claimed.

NumMaxRetries is the max times of doing retry.

We've completely processed all records in this shard.

ErrSequenceIDNotFound is returned by FetchCheckpoint when no SequenceID is found.

ErrShardNotAssigned is returned by ListActiveWorkers when no AssignedTo is found.

DynamoCheckpoint implements the Checkpoint interface using DynamoDB as a backend.

Checkpointer handles checkpointing when a record has been processed.