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https://issues.apache.org/jira/browse/HADOOP-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12503663
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Sameer Paranjpye commented on HADOOP-1470:
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>From what I've seen of the implementations of FSInputChecker and
>FSOutputSummer it looks like they can be very simply tweaked to handle the two
>cases of
a) parallel data and checksum streams and
b) a single stream with data and checksums interleaved
they can already handle the end-of-stream case where the number of bytes to be
checksummed is <= bytesPerChecksum
why not just tweak the existing implementations and make them capable of
handling a single stream with data and checksums interleaved?
The implementation could then be used by both ChecksumFilesystem the
DistributedFilesystem.
DFSInputStream would then instantiate a DFSBlockStream (a new class) wrap it in
an FSInputChecker and commence reading, it would re-initialize the input
checker with a new DFSBlockStream when the end of a block was reached or when
seek was called, the 'pread' case would need to be handled carefully.
I don't see the need for methods to read data and checksums independently of
each other.
> 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
>
> Attachments: genericChecksum.patch
>
>
> 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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