[jira] Issue Comment Edited: (HADOOP-1470) Rework FSInputChecker and FSOutputSummer to support checksum code sharing between ChecksumFileSystem and block level crc dfs

["Hairong Kuang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12502137 ] 

Hairong Kuang edited comment on HADOOP-1470 at 6/6/07 3:43 PM:
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The file ReadBuffer.java that Raghu submitted to HADOOP-1134 shows only the ChecksumException handling code. How about the checksum verification and checksum generation parts of code? I think they should also belong to the generic classes.

Let's suppose that the genric classes are Checker for reading and Summer for writing. Should each of these two classes contains two streams, one for data and one for checksum? Should these two streams be an abstraction of a block or a file?



 was:
The file ReadBuffer.java that Raghu submitted to HADOOP-1134 shows only the ChecksumException handling code. How about the checksum verification and checksum generation parts of code? I think they should also belong to the generic classes.

Let's suppose that the genric classes are Checker for reading and Summer for writing. Should these two classes contain two streams, one for data and one for checksum? Should these two streams be an abstraction of a block or a file?


> 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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