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https://issues.apache.org/jira/browse/FLINK-34704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17836083#comment-17836083
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Piotr Nowojski commented on FLINK-34704:
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{quote}
the checkpoint still happen when some user code is running.
{quote}
If you are talking about async user code from AWOP, that's not a problem and
never has been. When I'm talking about problems with state inconsistency of
upstream chained operators, that's exactly what I mean. Problem is for UPSTREAM
operator that is CHAINED with AWOP:
network input -> OperatorA -> AWOP -> network output
OperatorA's state can become corrupted/inconsistent if you allow for checkpoint
to happen while {{AWOP}} invokes {{.yield()}}. That's the whole point of the
yield to downstream (https://issues.apache.org/jira/browse/FLINK-13063). And
side note, it's not only a problem of {{AWOP}} but any operator that wants to
{{.yield()}}. Operators can only yield to downstream, which also means
checkpoints can not be executed, and it affects also firing timers.
I have a WIP FLIP-443 that will introduce a neat trick to allow operators to
return the execution back to {{StreamTask}} so that checkpoint can happen, but
AFAIU it has no application for the {{AWOP}}. When {{AWOP}} wants to
{{.yield()}}, it means it has no more space in the buffer to store any more
records. So we can not checkpoint {{AWOP}} until some buffer space will become
available. So {{AWOP}} needs to yield to downstream ({{.yield()}}) until buffer
space becomes available, return from the {{#processElement()}} call, and then
it needs to relay on a fix for FLINK-35051 for stream task to prioritise
performing a checkpoint over executing more records/mails.
> Process checkpoint barrier in AsyncWaitOperator when the element queue is full
> ------------------------------------------------------------------------------
>
> Key: FLINK-34704
> URL: https://issues.apache.org/jira/browse/FLINK-34704
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Task
> Reporter: Zakelly Lan
> Priority: Minor
>
> As discussed in
> https://lists.apache.org/thread/4f7ywn29kdv4302j2rq3fkxc6pc8myr2 . Maybe it
> is better to provide such a new `yield` that can process mail with low
> priority in the mailbox executor. More discussion needed.
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