Mailing-List: contact hdfs-issues-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: hdfs-issues@hadoop.apache.org
Date: Tue, 15 Jan 2013 19:14:13 +0000 (UTC)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12627554.1358212279453.139156.1358277253750@arcas>
In-Reply-To: <JIRA.12627554.1358212279453@arcas>
References: <JIRA.12627554.1358212279453@arcas>
Subject: [jira] [Commented] (HDFS-4403) DFSClient can infer checksum type
 when not provided by reading first byte
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit


    [ https://issues.apache.org/jira/browse/HDFS-4403?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13554175#comment-13554175 ] 

Todd Lipcon commented on HDFS-4403:
-----------------------------------

Hi Suresh. I don't see how that would be incompatible. You can add or remove defaults and maintain compatibility as far as I can imagine. What client/server combination would not work given this change?
                
> DFSClient can infer checksum type when not provided by reading first byte
> -------------------------------------------------------------------------
>
>                 Key: HDFS-4403
>                 URL: https://issues.apache.org/jira/browse/HDFS-4403
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs-client
>    Affects Versions: 2.0.2-alpha
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Minor
>         Attachments: hdfs-4403.txt
>
>
> HDFS-3177 added the checksum type to OpBlockChecksumResponseProto, but the new protobuf field is optional, with a default of CRC32. This means that this API, when used against an older cluster (like earlier 0.23 releases) will falsely return CRC32 even if that cluster has written files with CRC32C. This can cause issues for distcp, for example.
> Instead of defaulting the protobuf field to CRC32, we can leave it with no default, and if the OpBlockChecksumResponseProto has no checksum type set, the client can send OP_READ_BLOCK to read the first byte of the block, then grab the checksum type out of that response (which has always been present)

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira