Gera Shegalov created HADOOP-12326:
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             Summary: Implement ChecksumFileSystem#getFileChecksum equivalent 
to HDFS for easy check
                 Key: HADOOP-12326
                 URL: https://issues.apache.org/jira/browse/HADOOP-12326
             Project: Hadoop Common
          Issue Type: Improvement
          Components: fs
    Affects Versions: 2.7.1
            Reporter: Gera Shegalov
            Assignee: Gera Shegalov


If we have same-content files, one local and one remotely on HDFS (after 
downloading or uploading), getFileChecksum can provide a quick check whether 
they are consistent.  To this end, we can switch to CRC32C on local filesystem. 
The difference in block sizes does not matter, because for the local filesystem 
it's just a logical parameter.

{code}
$ hadoop fs -Dfs.local.block.size=134217728 -checksum file:${PWD}/part-m-00000 
part-m-00000
15/08/15 13:30:02 WARN util.NativeCodeLoader: Unable to load native-hadoop 
library for your platform... using builtin-java classes where applicable
file:///Users/gshegalov/workspace/hadoop-common/part-m-00000    
MD5-of-262144MD5-of-512CRC32C   
000002000000000000040000e84fb07f8c9d4ef3acb5d1983a7e2a68
part-m-00000    MD5-of-262144MD5-of-512CRC32C   
000002000000000000040000e84fb07f8c9d4ef3acb5d1983a7e2a68
{code}



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