Eugene Kirpichov created BEAM-3499:
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Summary: Watch can make no progress if a single poll takes more
than checkpoint interval
Key: BEAM-3499
URL: https://issues.apache.org/jira/browse/BEAM-3499
Project: Beam
Issue Type: Bug
Components: sdk-java-core
Reporter: Eugene Kirpichov
Assignee: Eugene Kirpichov
E.g. when using it to poll a filepattern with hundreds of thousands of files, a
single poll may take >10 seconds (default checkpoint interval in
OutputAndTimeBoundedSplittableProcessElementInvoker). Because of that, the
tracker (GrowthTracker) gets checkpointed before anything is added to it, i.e.
before
[https://github.com/apache/beam/blob/0d918b7cab8c4ccb2b5e050501327912161d40a7/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Watch.java#L727,]
at a moment when it doesn't contain any useful information, so the residual
checkpoint state is as empty as the initial one.
One possible fix to this is to change the SDF checkpointing strategy to have a
progress guarantee: e.g., start counting time from the moment the first block
is claimed, or allow the tracker to refuse checkpointing if nothing is claimed
yet, or something like that.
A workaround for users of this (primarily via FileIO.match().continuously()) is
to shard their filepattern into a set of finer-granularity filepatterns
matching fewer files, so that each match call takes less than 10 seconds.
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