[jira] [Commented] (FLINK-31610) Refactoring of LocalBufferPool

["Rui Fan (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-31610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17709173#comment-17709173 ] 

Rui Fan commented on FLINK-31610:
---------------------------------

Thanks [~akalash]  driving this JIRA, and thanks [~Weijie Guo] [~pnowojski]  's discussion. Sorry for the late response.

 
{quote}Consider such a scenario, the {{{}CurrentPoolSize = 5{}}}, {{{}numOfRequestedMemorySegments = 7{}}}, {{{}maxOverdraftBuffersPerGate = 2{}}}. If {{{}numberOfRequestedOverdraftMemorySegments = 0{}}}, then 2 buffers can be requested now. 

It only happens when poolSize changes.
{quote}
From this case and the definition of the overdraft buffer, it shouldn't be able to request now. General principle: new buffers can be requested when "{_}numOfRequestedMemorySegments + numberOfRequestedOverdraftMemorySegments < poolSize + maxOverdraftBuffersPerGate"{_}.

For the code design, [~Weijie Guo]  and me discussed it in this PR[1] before, I didn't find this case at that time. If the case can happen, I think we should convert _{{numberOfRequestedMemorySegments}}_ to {{_numberOfRequestedOverdraftMemorySegments_ when poolSize is decreased.}}

 
{quote}I can propose getting rid of numberOfRequestedOverdraftMemorySegments and using existing numberOfRequestedMemorySegments instead.
{quote}
Overall, it think it is feasible. The new buffers can be requested when {_}"numberOfRequestedMemorySegments < poolSize + maxOverdraftBuffersPerGate"{_}:
 * When _numberOfRequestedMemorySegments <= poolSize,_ all buffers are ordinary buffer 
 * When _numberOfRequestedMemorySegments > poolSize,_ the `{_}ordinary buffer size = poolSize`{_}, and `{_}the overdraft buffer size = numberOfRequestedMemorySegments - poolSize`{_}

 

Please correct me if I'm wrong.

 

[1] https://github.com/apache/flink/pull/22084/files#r1128926904

> Refactoring of LocalBufferPool
> ------------------------------
>
>                 Key: FLINK-31610
>                 URL: https://issues.apache.org/jira/browse/FLINK-31610
>             Project: Flink
>          Issue Type: Improvement
>          Components: Runtime / Network
>    Affects Versions: 1.17.0
>            Reporter: Anton Kalashnikov
>            Priority: Major
>
> FLINK-31293 bug highlighted the issue with the internal mutual consistency of different fields in LocalBufferPool. ex.:
> -  `numberOfRequestedOverdraftMemorySegments`
> -  `numberOfRequestedMemorySegments`
> -  `availableMemorySegment`
> -  `currentPoolSize`
> Most of the problem was fixed already(I hope) but it is a good idea to reorganize the code in such a way that all invariants between all fields inside will be clearly determined and difficult to break.
> As one example I can propose getting rid of numberOfRequestedOverdraftMemorySegments and using existing numberOfRequestedMemorySegments instead. That means:
> - the pool will be available when `!availableMemorySegments.isEmpty() && unavailableSubpartitionsCount == 0`
> - we don't request a new `ordinary` buffer when `numberOfRequestedMemorySegments >=  currentPoolSize` but we request the overdraft buffer instead
> - `setNumBuffers` should work automatically without any changes
> I think we can come up with a couple of such improvements to simplify the code.



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