[jira] [Commented] (FLINK-17860) Recursively remove channel state directories

["Roman Khachatryan (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-17860?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17113856#comment-17113856 ] 

Roman Khachatryan commented on FLINK-17860:
-------------------------------------------

I think FLINK-13856 describes a more general problem (any state handle types). 

This issue is about channel state handles only. They are:
 * always located on file system (so we don't miss anything by replacing discard() call with recursive delete)
 * their number depends on stream properties (backpressure), not operator logic
 * not incremental

 

> Recursively remove channel state directories
> --------------------------------------------
>
>                 Key: FLINK-17860
>                 URL: https://issues.apache.org/jira/browse/FLINK-17860
>             Project: Flink
>          Issue Type: Improvement
>          Components: Runtime / Checkpointing
>    Affects Versions: 1.11.0
>            Reporter: Roman Khachatryan
>            Assignee: Roman Khachatryan
>            Priority: Critical
>             Fix For: 1.11.0
>
>
> With a high degree of parallelism, we end up with n*s number of files in each checkpoint (n = parallelism, s = stages). Writing them if fast (from many subtasks), removing them is slow (from JM).
> This can't be mitigated by state.backend.fs.memory-threshold because most states are ten to hundreds Mb.
>  
> Instead of going through them 1 by 1, we could remove the directory recursively.
>  
> The easiest way is to remove channelStateHandle.discard() calls and use isRecursive=true  in FsCompletedCheckpointStorageLocation.disposeStorageLocation.
> Note: with the current isRecursive=false there will be an exception if there are any files left under that folder.
>  
> This can be extended to other state handles in future as well.



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