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From "Luke Cwik (JIRA)" <>
Subject [jira] [Commented] (BEAM-758) Per-step, per-execution nonce
Date Mon, 17 Oct 2016 17:07:58 GMT


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:
>             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

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