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https://issues.apache.org/jira/browse/BEAM-13203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17441190#comment-17441190
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Etienne Chauchot commented on BEAM-13203:
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yes, proper async mechanism with retrials, limited buffered requests and timed
out wait for async response seem to be necessary.
If the write is backpressured, there is no way to slow down the source (because
its watermark will got forward) so the records will be buffered in the write
operation indeed
> Potential data loss when using SnsIO.writeAsync
> -----------------------------------------------
>
> Key: BEAM-13203
> URL: https://issues.apache.org/jira/browse/BEAM-13203
> Project: Beam
> Issue Type: Bug
> Components: io-java-aws
> Reporter: Moritz Mack
> Priority: P0
>
> This needs to be investigated, reading the code suggests we might be losing
> data under certain conditions e.g. when terminating the pipeline. The async
> processing model here is far too simplistic.
> The bundle won't ever know about pending writes and won't block to wait for
> any such operation. The same way exceptions are thrown into nowhere. Test
> cases don't capture this as they operate on completed futures only (so
> exceptions in the callbacks get thrown on the thread of processElement).
> {code:java}
> client.publish(publishRequest).whenComplete((response, ex) -> {
> if (ex == null) {
> SnsResponse<T> snsResponse = SnsResponse.of(context.element(), response);
> context.output(snsResponse);
> } else {
> LOG.error("Error while publishing request to SNS", ex);
> throw new SnsWriteException("Error while publishing request to SNS", ex);
> }
> }); {code}
> Also, this entirely removes backpressure from a stream. When used with a much
> faster source we will continue to accumulate more and more memory as the
> number of concurrent pending async operations is not limited.
> Spotify's scio contains a
> [JavaAsyncDoFn|https://github.com/spotify/scio/blob/main/scio-core/src/main/java/com/spotify/scio/transforms/JavaAsyncDoFn.java]
> that illustrates how it can be done.
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