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https://issues.apache.org/jira/browse/FLINK-3257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15688077#comment-15688077
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ASF GitHub Bot commented on FLINK-3257:
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Github user senorcarbone commented on the issue:
https://github.com/apache/flink/pull/1668
Ok, so I am progressing this a bit independently from the termination stuff
and then we rebase to the first PR that is merged. I just changed everything
and rebased to the current master.
Some notable changes:
- The `StreamIterationCheckpointingITCase` is not made deterministic, it
fails after the first successful checkpoint once and the jobs stops after
everything has been recovered appropriately.
- I am now using ListState which is supposed to work like a charm with the
rocksdb file backend. Note that with the default in-memory backend there is a
high chance to get issues given the low memory capacity that it is given by
default.
- One tricky part that can be potentially done better is the way I set the
logger in the StreamIterationHead (had to change the head op field access to
`protected` in the OperatorChain)
Whenever you find time go ahead and check it out. It passes my super-strict
test which is a good thing. :)
> Add Exactly-Once Processing Guarantees in Iterative DataStream Jobs
> -------------------------------------------------------------------
>
> Key: FLINK-3257
> URL: https://issues.apache.org/jira/browse/FLINK-3257
> Project: Flink
> Issue Type: Improvement
> Reporter: Paris Carbone
> Assignee: Paris Carbone
>
> The current snapshotting algorithm cannot support cycles in the execution
> graph. An alternative scheme can potentially include records in-transit
> through the back-edges of a cyclic execution graph (ABS [1]) to achieve the
> same guarantees.
> One straightforward implementation of ABS for cyclic graphs can work as
> follows along the lines:
> 1) Upon triggering a barrier in an IterationHead from the TaskManager start
> block output and start upstream backup of all records forwarded from the
> respective IterationSink.
> 2) The IterationSink should eventually forward the current snapshotting epoch
> barrier to the IterationSource.
> 3) Upon receiving a barrier from the IterationSink, the IterationSource
> should finalize the snapshot, unblock its output and emit all records
> in-transit in FIFO order and continue the usual execution.
> --
> Upon restart the IterationSource should emit all records from the injected
> snapshot first and then continue its usual execution.
> Several optimisations and slight variations can be potentially achieved but
> this can be the initial implementation take.
> [1] http://arxiv.org/abs/1506.08603
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