Luke Cwik commented on BEAM-758:

Several runners have the concept of a job or pipeline id, using a stable hash 
of the job or pipeline id could be used to generate the nonce.

Currently we expose job name within PipelineOptions, we could also expose the 
concept of job id which is populated by a runner and is expected to uniquely 
identify the job with respect to the runner if the runner supports running 
multiple jobs at the same time.

> Per-step, per-execution nonce
> -----------------------------
>                 Key: BEAM-758
>                 URL: https://issues.apache.org/jira/browse/BEAM-758
>             Project: Beam
>          Issue Type: Improvement
>          Components: sdk-java-core
>    Affects Versions: Not applicable
>            Reporter: Daniel Halperin
> In the forthcoming runner API, a user will be able to save a pipeline to JSON 
> and then run it repeatedly.
> Many pieces of code (e.g., BigQueryIO.Read or Write) rely on a single random 
> value (nonce). These values are typically generated at apply time, so that 
> they are deterministic (don't change across retries of DoFns) and global (are 
> the same across all workers).
> However, once the runner API lands the existing code would result in the same 
> nonce being reused across jobs. Other possible solutions:
> * Generate nonce in {{Create(1) | ParDo}} then use this as a side input. 
> Should work, as along as side inputs are actually checkpointed. But does not 
> work for {{BoundedSource}}.
> * If a nonce is only needed for the lifetime of one bundle, can be generated 
> in {{startBundle}} and used in {{finishBundle}} [or {{tearDown}}].
> * Add some context somewhere that lets user code access unique step name, and 
> somehow generate a nonce consistently e.g. by hashing. Will usually work, but 
> this is similarly not available to sources.
> Another Q: I'm not sure we have a good way to generate nonces in unbounded 
> pipelines -- we probably need one. This would enable us to, e.g., use 
> {{BigQueryIO.Write}} in an unbounded pipeline [if we had, e.g., exactly-once 
> triggering per window]. Or generalizing to multiple firings...

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