hadoop-hdfs-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1630) Checksum fsedits
Date Thu, 17 Feb 2011 22:11:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12996121#comment-12996121
] 

Hairong Kuang commented on HDFS-1630:
-------------------------------------

I did some experiments with MD5. For every transaction, a MD5 digest (16 bytes) is calculated.
But to save the disk overhead, only half of the digest (8 bytes) is saved to the fssedit log.
I observed only 2% overhead for directory creations and deletions in fsnamesystem for an average
transaction size of 100 bytes. This seems negligible.

> the stream to the secondary/backup node should also be checksummed to detect...
If we have checksum for each fsedit transaction, I do not see the need to checksum the stream.
The only error case that could not be detected by per transaction checksum is that the edit
log gets truncated at a transaction boundary. However, SNN does validate the edit log size.
So the truncation can be also detected.

> Checksum fsedits
> ----------------
>
>                 Key: HDFS-1630
>                 URL: https://issues.apache.org/jira/browse/HDFS-1630
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>
> HDFS-903 calculates a MD5 checksum to a saved image, so that we could verify the integrity
of the image at the loading time.
> The other half of the story is how to verify fsedits. Similarly we could use the checksum
approach. But since a fsedit file is growing constantly, a checksum per file does not work.
I am thinking to add a checksum per transaction. Is it doable or too expensive?

-- 
This message is automatically generated by JIRA.
-
For more information on JIRA, see: http://www.atlassian.com/software/jira

        

Mime
View raw message