[
https://issues.apache.org/jira/browse/FLINK-27155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17526973#comment-17526973
]
Yun Tang commented on FLINK-27155:
----------------------------------
> I think Yun Tang means waiting for all task of a TM to switch from
> INITIALIZING to RUNNING.
> I think it could be problematic, because the set of tasks is dynamic.
>From my understanding, the task manager could be able to know that all tasks
>has changed to RUNNING status.
> I think task in RUNNING state not mean we can clean up the cache file,
> because changelog download and applying to delegated backend is in RUNNING
> state.
Applying the changelogs happens during changelog restore phase, which is in the
task INITIALIZATING state (not the RUNNING state), that's why I think we can
safely discard downloaded files as the phase has completed.
[~Feifan Wang] do you think you can provide a design doc to include all
discussions here?
> 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: Sub-task
> Components: Runtime / State Backends
> Reporter: Feifan Wang
> Assignee: Feifan Wang
> Priority: Major
> Fix For: 1.16.0
>
>
> 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 ?
--
This message was sent by Atlassian Jira
(v8.20.7#820007)
