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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1470) Rework FSInputChecker and FSOutputSummer to support checksum code sharing between ChecksumFileSystem and block level crc dfs
Date Wed, 06 Jun 2007 19:15:26 GMT
Rework FSInputChecker and FSOutputSummer to support checksum code sharing between ChecksumFileSystem
and block level crc dfs
----------------------------------------------------------------------------------------------------------------------------

                 Key: HADOOP-1470
                 URL: https://issues.apache.org/jira/browse/HADOOP-1470
             Project: Hadoop
          Issue Type: Improvement
          Components: fs
    Affects Versions: 0.12.3
            Reporter: Hairong Kuang
            Assignee: Hairong Kuang
             Fix For: 0.14.0


Comment from Doug in HADOOP-1134:
I'd prefer it if the CRC code could be shared with CheckSumFileSystem. In particular, it seems
to me that FSInputChecker and FSOutputSummer could be extended to support pluggable sources
and sinks for checksums, respectively, and DFSDataInputStream and DFSDataOutputStream could
use these. Advantages of this are: (a) single implementation of checksum logic to debug and
maintain; (b) keeps checksumming as close to possible to data generation and use. This patch
computes checksums after data has been buffered, and validates them before it is buffered.
We sometimes use large buffers and would like to guard against in-memory errors. The current
checksum code catches a lot of such errors. So we should compute checksums after minimal buffering
(just bytesPerChecksum, ideally) and validate them at the last possible moment (e.g., through
the use of a small final buffer with a larger buffer behind it). I do not think this will
significantly affect performance, and data integrity is a high priority. 


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