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