[jira] [Created] (HADOOP-18296) Memory fragmentation in ChecksumFileSystem Vectored IO implementation.

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

Mukund Thakur created HADOOP-18296:
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             Summary: Memory fragmentation in ChecksumFileSystem Vectored IO implementation.
                 Key: HADOOP-18296
                 URL: https://issues.apache.org/jira/browse/HADOOP-18296
             Project: Hadoop Common
          Issue Type: Sub-task
          Components: common
    Affects Versions: 3.4.0
            Reporter: Mukund Thakur


As we have implemented merging of ranges in the ChecksumFSInputChecker implementation of vectored IO api, it can lead to memory fragmentation. Let me explain by example.

 

Suppose client requests for 3 ranges. 

0-500, 700-1000 and 1200-1500.

Now because of merging, all the above ranges will get merged into one and we will allocate a big byte buffer of 0-1500 size but return sliced byte buffers for the desired ranges.

Now once the client is done reading all the ranges, it will only be able to free the memory for requested ranges and memory of the gaps will never be released for eg here (500-700 and 1000-1200).

 

Note this only happens for direct byte buffers.



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