[jira] [Created] (FLINK-26762) Add the overdraft buffer in BufferPool to reduce unaligned checkpoint being blocked

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

fanrui created FLINK-26762:
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             Summary: Add the overdraft buffer in BufferPool to reduce unaligned checkpoint being blocked
                 Key: FLINK-26762
                 URL: https://issues.apache.org/jira/browse/FLINK-26762
             Project: Flink
          Issue Type: Improvement
          Components: Runtime / Checkpointing, Runtime / Network
    Affects Versions: 1.14.0, 1.13.0, 1.15.0
            Reporter: fanrui
             Fix For: 1.16.0


In some past JIRAs of Unaligned Checkpoint, the community has added the  recordWriter.isAvaliable() to reduce block for single record write. But for large record, flatmap or broadcast watermark, they may need more buffer.

Can we add the overdraft buffer in BufferPool to reduce unaligned checkpoint being blocked? 
h2. Overdraft Buffer mechanism

Add the configuration of 'taskmanager.network.memory.overdraft-buffers-per-gate=5'. 

When requestMemory is called and the bufferPool is insufficient, the bufferPool will allow the Task to overdraw up to 5 MemorySegments. And bufferPool will be unavailable until all overdrawn buffers are consumed by downstream tasks. Then the task will wait for bufferPool being available.

From the above, we have the following benefits:
 * For scenarios that require multiple buffers, the Task releases the Checkpoint lock, so the Unaligned Checkpoint can be completed quickly.
 * We can control the memory usage to prevent memory leak.
 * It just needs a litter memory, and can improve the stability of the Task under back pressure.
 * Users can increase the overdraft-buffers to adapt the scenarios that require more buffers.

 

Masters, please correct me if I'm wrong, thanks a lot.



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