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https://issues.apache.org/jira/browse/HADOOP-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12502148
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Raghu Angadi commented on HADOOP-1470:
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> In the block-level-crc dfs, do we allow different values of bytesPerSum for
> blocks in a file?
Yes. Though there is no way to do this now. Also we don't enforce that each
block to have same {{bps}} for a file. So theoretical yes.
> Do we allow different block size for blocks in a file?
No. Just like current DFS. i.e. this is not a block-level-crc specific issue.
bq. If data are checksumed at the FileSystem level, there is another complexity
in the block-level-crc dfs. When a block size is not a multiple of bytesPerSum,
we also need to output/verify checksum at the end of each block. So it is
harder to decide checksumChunk boundaries.
good point. Yes. This will further influence ChecksumFileSystem implementation.
This inter-(dependency and influence) between ChecksumFS and DFS could
potentially further increase with this jira,
> 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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