Data engineering·Time and correctness in streams
the operator's state is an embedded key-value store on local disk, and losing that disk means restoring from remote storage before anything can run.
State backend
Also calledstate store, embedded store
Where a streaming job's state actually lives — on the JVM heap for speed, or in an embedded on-disk store for size, backed up to object storage for durability. The choice sets your ceiling on state size and your recovery time, and it is nearly always the thing behind 'why is this job slow' once the state exceeds memory. It is worth knowing because state operations are invisible in the job's logic and dominant in its performance profile.