resumable

Resumable describes a property of systems and processes that can be paused and later continued from where they left off, rather than starting over. Achieving resumability typically relies on persistent state, checkpoints, and mechanisms that track progress so the operation can proceed after an interruption.

Common techniques include checkpointing, which saves the current state to durable storage; chunking, which divides data into parts that can be transferred or processed independently; and the use of identifiers or tokens that allow a task to be rehydrated and resumed. Resumable transfers often require coordination between client and server to verify integrity and avoid duplicate work.

In practice, resumable functionality appears in several domains. Resumable downloads use techniques such as HTTP range requests to fetch only the remaining portions of a file after a network interruption. Resumable uploads employ chunked or multipart uploading, sometimes using protocols like tus, which manage uploaded chunks and a reference token so a user can resume from the last acknowledged part. Long-running data processing and machine learning workflows implement checkpointing to save progress and enable recovery after failures, reducing wasted computation.

Benefits of resumability include increased resilience to network or hardware failures, more efficient use of bandwidth, and improved user experience in environments with unreliable connectivity. Challenges involve maintaining reliable state, ensuring data integrity, and managing security and complexity.

Related concepts include checkpointing, partial content transfers, and idempotent operations. Examples of real-world implementations include resumable uploads via protocols like tus and HTTP range-based download methods.