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From "nkeywal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3702) Add an option for NOT writing the blocks locally if there is a datanode on the same box as the client
Date Wed, 25 Jul 2012 16:15:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422372#comment-13422372
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nkeywal commented on HDFS-3702:
-------------------------------

For a file open in writing, we will start with a call to ipc.Client to get the last block
length. The timeout in hdfs 1.0.3 is harcoded to 20s (fixed in HADOOP-7397). Hence, anyway,
HDFS-3704, but we can also hit HDFS-3701 at this point, so it also a question of data loss.
That's why we need to fix (HDFS-3701 and (HDFS-3702 or/and HDFS-3705 or/and HDFS-3703)).

For reducing the connect timeout, are you speaking about dfs.socket.timeout? Is there a way
to change it for connect timeout only?

                
> Add an option for NOT writing the blocks locally if there is a datanode on the same box
as the client
> -----------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-3702
>                 URL: https://issues.apache.org/jira/browse/HDFS-3702
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>    Affects Versions: 1.0.3, 2.0.0-alpha
>            Reporter: nkeywal
>            Priority: Minor
>
> This is useful for Write-Ahead-Logs: these files are writen for recovery only, and are
not read when there are no failures.
> Taking HBase as an example, these files will be read only if the process that wrote them
(the 'HBase regionserver') dies. This will likely come from a hardware failure, hence the
corresponding datanode will be dead as well. So we're writing 3 replicas, but in reality only
2 of them are really useful.

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