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[jira] [Created] (FLINK-10981) Add or modify metrics to show the maximum usage of InputBufferPool/OutputBufferPool to help debugging back pressure


Yun Gao created FLINK-10981:
-------------------------------

             Summary: Add or modify metrics to show the maximum usage of InputBufferPool/OutputBufferPool to help debugging back pressure
                 Key: FLINK-10981
                 URL: https://issues.apache.org/jira/browse/FLINK-10981
             Project: Flink
          Issue Type: Improvement
          Components: Metrics, Network
            Reporter: Yun Gao
            Assignee: Yun Gao


Currently the network layer has provided two metrics items, namely _InputBufferPoolUsageGauge_ and _OutputBufferPoolUsageGauge_ to show the usage of input buffer pool and output buffer pool. When there are multiple inputs(SingleInputGate) or __ outputs(ResultPartition), the two metrics items show their average usage. 

 

However, we found that the maximum usage of all the InputBufferPool or OutputBufferPool is also useful in debugging back pressure. Suppose we have a job with the following job graph:

 
{code:java}
          F     
           \
            \
            _\/      
A ---> B ----> C ---> D
       \
        \
         \-> E 
         {code}
Besides, also suppose D is very slow and thus cause back pressure, but E is very fast and F outputs few records, thus the usage of the corresponding input/output buffer pool is almost 0.

 

Then the average input/output buffer usage of each task will be:

 
{code:java}
A(100%) --> (100%) B (50%) --> (50%) C (100%) --> (100%) D
{code}
 

 

But the maximum input/output buffer usage of each task will be:

 
{code:java}
A(100%) --> (100%) B (100%) --> (100%) C (100%) --> (100%) D
{code}
Users will be able to find the slowest task by finding the first task whose input buffer usage is 100% but output usage is less than 100%.

 

 

If it is reasonable to show the maximum input/output buffer usage, I think there may be three options:
 # Modify the current computation logic of _InputBufferPoolUsageGauge_ and _OutputBufferPoolUsageGauge._
 # Add two __ new metrics items I_nputBufferPoolMaxUsageGauge and OutputBufferPoolUsageGauge._
 # Try to show distinct usage for each input/output buffer pool.

and I think maybe the second option is the most preferred. 

 

How do you think about that?

 

 

 



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