[
https://issues.apache.org/jira/browse/FLINK-10930?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16701774#comment-16701774
]
Stephan Ewen commented on FLINK-10930:
--------------------------------------
Sorry, the first part was a typo on my side. It should have meant that "the
checkpoint cannot complete anyways, because it is already timed out". So the
failure is not a problem per se.
I think changing the layout is fixing the problem at the wrong end, it is
trying to mitigate the symptom rather than fixing the cause.
My feeling is that the right approach is to better handle what failures do to
checkpoints:
- A failure when materializing the checkpoint results in a "checkpoint
declined message", but should never trigger a task failure on the taskmanager
directly.
- The checkpoint coordinator receives the decline message. If the checkpoint
is already disposed (timeout or another failure), then no problem, simply
ignore the exception (clean up state chunk).
- If the checkpoint fails because of the decline message, the coordinator can
decide whether this should cause a failure of the task or not (this also
enables strategies like "fail only of n consecutive checkpoints failed").
> Refactor checkpoint directory layout
> ------------------------------------
>
> Key: FLINK-10930
> URL: https://issues.apache.org/jira/browse/FLINK-10930
> Project: Flink
> Issue Type: Improvement
> Components: State Backends, Checkpointing
> Affects Versions: 1.8.0
> Reporter: Yun Tang
> Assignee: Yun Tang
> Priority: Major
> Fix For: 1.8.0
>
>
> The current checkpoint directory layout is introduced from FLINK-8531 with
> three different scopes for tasks:
> * *EXCLUSIVE* is for state that belongs to one checkpoint only, meta data
> and operator state files.
> * *SHARED* is for state that is possibly part of multiple checkpoints
> * *TASKOWNED* is for state that must never by dropped by the jobManager.
> {code:java}
> /user-defined-dir/{job-id}
> |
> +-- shared/
> +-- taskowned/
> +-- chk-1/ // metadata and operator-state files
> +-- chk-2/
> ...{code}
> If we just retain one complete checkpoint, the expected exclusive directory,
> which is the {{chk-id}} checkpoint directory, should only be one left.
> However, as FLINK-10855 interpreted, the failed/expired checkpoint
> directories would also be left. This is really confusing for users who [uses
> externalized checkpoint to resume
> job|https://ci.apache.org/projects/flink/flink-docs-release-1.6/ops/state/checkpoints.html#resuming-from-a-retained-checkpoint],
> not to mention the checkpoint directory resource leak.
> As far as I could know, if the {{chk-id}} checkpoint directory still
> contains the operator state files, I have no idea how to clean the useless
> {{chk-id}} checkpoint directory gracefully. Once job manager dispose the
> failed/expired checkpoint, the target {{chk-id}} checkpoint directory would
> be deleted by JM. However, this directory would also be create by tasks who
> having not reported to JM. When {{checkpoint coordinator}} received those
> late expired tasks, it would discard those useless handles. However, if JM
> also plans to delete the empty parent folder, which is already unsupported
> after FLINK-8540, another task uploading operator state files would meet
> exception due to its writing target's parent directory has just been removed.
> Currently, we handle task checkpoint failure as task failure and the whole
> job would failover which is not we want.
> From what I see, I plan to separate *EXCLUSIVE* directory into two kind of
> exclusive directories, one is still several {{chk-id}} checkpoint directories
> but only contains its exclusive {{meta data}}, the other is just one
> directory named {{exclusive}} which containing the operator state files.
> Operator state files are exclusive to just one specified checkpoint, we could
> also add {{checkpoint-id}} within their file name to let users easily clean
> up.
> The refactored directory layout should be :
> {code:java}
> /user-defined-dir/{job-id}
> |
> +-- shared/
> +-- taskowned/
> +-- exclusive/ // operator state files
> +-- chk-1/ // metadata
> +-- chk-2/
> ...{code}
>
> This new directory layout would not affect users who use external checkpoint
> to resume jobs, since they still just give
> {{/user-defined-dir/job-id/chk-id}} path to resume job.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
