Glen Geng created HDDS-4228:
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             Summary: ALLOCATE_BLOCK of scm audit log miss num
                 Key: HDDS-4228
                 URL: https://issues.apache.org/jira/browse/HDDS-4228
             Project: Hadoop Distributed Data Store
          Issue Type: Improvement
            Reporter: Glen Geng
            Assignee: Marton Elek


Teragen reported to be slow with low number of mappers compared to HDFS.

In my test (one pipeline, 3 yarn nodes) 10 g teragen with HDFS was ~3 mins but 
with Ozone it was 6 mins. It could be fixed with using more mappers, but when I 
investigated the execution I found a few problems reagrding to the BufferPool 
management.

 1. IncrementalChunkBuffer is slow and it might not be required as BufferPool 
itself is incremental
 2. For each write operation the bufferPool.allocateBufferIfNeeded is called 
which can be a slow operation (positions should be calculated).
 3. There is no explicit support for write(byte) operations

In the flamegraph it's clearly visible that with low number of mappers the 
client is busy with buffer operations. After the patch the rpc call and the 
checksum calculation give the majority of the time. 



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