Rework FSInputChecker and FSOutputSummer to support checksum code sharing
between ChecksumFileSystem and block level crc dfs
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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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