1996fanrui commented on PR #54:
URL: https://github.com/apache/flink-benchmarks/pull/54#issuecomment-1103807858

   By the way, I found an interesting point while playing the benchmark. That 
is, the UNALIGNED_RECORD_SIZE is 1KB in the benchmark(In production, the single 
record size of many flink jobs is less than 1KB.). If UNALIGNED_RECORD_SIZE is 
reduced, UNALIGNED will perform worse, but UNALIGNED_OVERDRAFT performance is 
not affected. 
   
   Because flatmap requires 5 output buffers to process a single record, it 
will wait for 5 buffers to be processed downstream. If the record size is 
smaller, the 5 output buffers will hold more records, and  the downstream Task 
will take longer to process these records. But UNALIGNED_OVERDRAFT allows 
buffers to be overdrawn, so the upstream does not need to wait for the 
downstream to process 5 buffers.


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