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https://issues.apache.org/jira/browse/FLINK-26790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17513247#comment-17513247
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Piotr Nowojski commented on FLINK-26790:
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I think [~assassinj]'s confusion is about the picture. On the first figure
captured "on first barrier", the checkpoint barrier for the lower connection is
in the middle of the output buffers (between buffers "e" and "d"), which
contradicts what is described below:
{quote}
by adding it to the end of the output buffers.
{quote}
I think indeed the graphic should be changed somehow.
I think I understand the [~arvid]'s intention behind it, that it was supposed
to depict a scenario where two checkpoint barriers from two different upstream
operators are arriving at different time, and the second channel is keep
persisting the in-flight data until it receives it's checkpoint barrier, but
indeed that's misleading as it is. Especially that it shows two operators
connected to each other via two channels? Which apart of some esoteric scenario
with for example union-ing output and side output of the same operator is
impossible to achieve.
I would either simplify this graph, and focus on single input/output channel
case (parallelism = 1), or keep it with upstream parallelism = 2, but then:
# Clearly adding one more upstream operator
# Adding one more extra step, where in the first figure only first upstream
operator inject checkpoint barrier, and in the next figure second upstream
operator is doing it
WDYT?
> Description image about Unaligned Checkpointing maybe incorrect.
> ----------------------------------------------------------------
>
> Key: FLINK-26790
> URL: https://issues.apache.org/jira/browse/FLINK-26790
> Project: Flink
> Issue Type: Improvement
> Components: Documentation
> Affects Versions: 1.13.6, 1.14.4
> Reporter: jinghaihang
> Priority: Minor
> Attachments: image-2022-03-22-11-12-20-025.png
>
>
> Due to the second description ：
> * It immediately forwards the barrier to the downstream operator by adding
> it to the end of the output buffers.
> so i think the picture maybe misleading readers that barrier will not appear
> in the middle of the data stream.
>
> !image-2022-03-22-11-12-20-025.png|width=599,height=303!
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