[FLINK-24690] Clarification of buffer size threshold calculation in BufferDebloater

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.14.0
• Fix Version/s: 1.14.3, 1.15.0
• Component/s: Runtime / Network
• Labels: pull-request-available
• Assignee: Anton Kalashnikov
• Reporter: Anton Kalashnikov
• Created: 29/Oct/21 06:21
• Updated: 15/Dec/21 01:44
• Resolved: 15/Nov/21 07:37

Description

It looks like that the variable `skipUpdate` in BufferDebloater#recalculateBufferSize is calculated in a not obvious way.

For example if `taskmanager.network.memory.buffer-debloat.threshold-percentages` is set to 50(means 50%) then it will be something like:

• 32000 -> 16000(possible)
• 32000 -> 17000(not possible)
• 16000 -> 24000(not possible) - but 16000 + 50%  = 24000
• 16000 -> 32000(only this possible)

This happens because the algorithm takes into account only the largest value. So in example of `16000 -> 24000` it would calculate 50% of 24000 so only transit from 12000 -> 24000 possible. 

In general, this approach is not so bad especially on small values (instead of 256  ->374, the minimum possible transit is 256 -> 512). But we should clarify it somewhere with test or javadoc or both. Also, we can discuss changing this algorithm to a more natural implementation.

 

Issue Links

• links to: GitHub Pull Request #17737
• links to: GitHub Pull Request #17780