hadoop-common-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1470) Rework FSInputChecker and FSOutputSummer to support checksum code sharing between ChecksumFileSystem and block level crc dfs
Date Tue, 12 Jun 2007 04:57:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12503725
] 

Raghu Angadi commented on HADOOP-1470:
--------------------------------------

I will summarize couple of approaches discussed. I was looking at the ChecksumFS to see how
the approaches fit and noticed that current pread ({{read(position, buf, off, len)}})  silently
returns unchecked data. Should I file a jira on this? Not sure if pread() is used anywhere.


With block CRCs, pread() on DistributedFS works ok but in the code I have now does not deal
with checksum errors properly (SeekToNewSource() messes up state). The new proposal should
enable us to implement pread() without much effort both ChecksumFS and DistributedFS.

Both preads can be fixed by locking the input stream and doing a '{{ seek(position); read();
seek(oldPos)}}'. But I think pread() is not supposed to block a sequential read(), and hopefully
avoid reopening underlying file (in DFS case not do another open()).



> 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. 

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


Mime
View raw message