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https://issues.apache.org/jira/browse/HADOOP-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12502533
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Doug Cutting commented on HADOOP-1470:
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> I don't agree with 'it is good enough until it is extremely difficult to use'
Who has argued for that? We're just trying to avoid duplicating some subtle
logic. I don't think you've demonstrated that using a generic checksummer will
make things significantly more complex in HDFS. I don't see that it adds
significant complexity to make the data and checksums appear as separate input
streams. Or, if you think that model is broken, propose another.
> I surely don't think it is an improvement over FSInputChecker which, I think,
> was not explicitly designed to be general purpose checker.
So what are you arguing? That it's a bad general purpose checker? If so, then
propose an improvement. Or that it's impossible to create a general purpose
checker that's easy for you to use? That seems unlikely, but we'll only find
out by trying, no?
> 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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