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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1707) Remove the DFS Client disk-based cache
Date Tue, 06 Nov 2007 00:12:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1707?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540308
] 

dhruba borthakur commented on HADOOP-1707:
------------------------------------------

In the current trunk, the first datanode in the pipeline sets a timeout of 2 minutes. The
second datanode sets a timeout of 1 minute, and so on. If a datanode does not receive a response
from a downstream datanode within this timeout period, it declared the downsteam data as dead.

In this patch for removing the client-side-disk buffer, the connection between datanodes in
the pipeline could remain open for extended periods of time, especially for clients that are
producing output slowly. I propose that we change the timeouts to behave as follows:

1. Each datanode in the pipeline has the same timeout of 1 minute. If a datanode does not
receive a response from a downstream datanode in 1 minute, it declares the downstream datanode
as dead.
2. Each datanode sends a heartbeat message to the upstream datanode once every half-timeout-period.

> Remove the DFS Client disk-based cache
> --------------------------------------
>
>                 Key: HADOOP-1707
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1707
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>             Fix For: 0.16.0
>
>         Attachments: clientDiskBuffer.patch, clientDiskBuffer2.patch
>
>
> The DFS client currently uses a staging file on local disk to cache all user-writes to
a file. When the staging file accumulates 1 block worth of data, its contents are flushed
to a HDFS datanode. These operations occur sequentially.
> A simple optimization of allowing the user to write to another staging file while simultaneously
uploading the contents of the first staging file to HDFS will improve file-upload performance.

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