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Posted to issues@flink.apache.org by "Yuan Mei (Jira)" <ji...@apache.org> on 2022/04/10 09:10:00 UTC
[jira] [Commented] (FLINK-27155) Reduce multiple reads to the same Changelog file in the same taskmanager during restore
[ https://issues.apache.org/jira/browse/FLINK-27155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17520127#comment-17520127 ]
Yuan Mei commented on FLINK-27155:
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Hey [~Feifan Wang] , thanks for the proposal.
Task Local Recovery will be supported in v2, I think that can partially resolve the problem
Indeed, downloading the same files times does not sound necessary.
> Reduce multiple reads to the same Changelog file in the same taskmanager during restore
> ---------------------------------------------------------------------------------------
>
> Key: FLINK-27155
> URL: https://issues.apache.org/jira/browse/FLINK-27155
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Checkpointing, Runtime / State Backends
> Reporter: Feifan Wang
> Priority: Major
>
> h3. Background
> In the current implementation, State changes of different operators in the same taskmanager may be written to the same changelog file, which effectively reduces the number of files and requests to DFS.
> But on the other hand, the current implementation also reads the same changelog file multiple times on recovery. More specifically, the number of times the same changelog file is accessed is related to the number of ChangeSets contained in it. And since each read needs to skip the preceding bytes, this network traffic is also wasted.
> The result is a lot of unnecessary request to DFS when there are multiple slots and keyed state in the same taskmanager.
> h3. Proposal
> We can reduce multiple reads to the same changelog file in the same taskmanager during restore.
> One possible approach is to read the changelog file all at once and cache it in memory or local file for a period of time when reading the changelog file.
> I think this could be a subtask of [v2 FLIP-158: Generalized incremental checkpoints|https://issues.apache.org/jira/browse/FLINK-25842] .
> Hi [~ym] , [~roman] how do you think about ?
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