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Date: Mon, 13 Oct 2008 06:00:44 -0700 (PDT)
From: "Brian Bockelman (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-4397) fuse-dfs causes corruptions on
 multi-threaded access
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    [ https://issues.apache.org/jira/browse/HADOOP-4397?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12639041#action_12639041 ] 

Brian Bockelman commented on HADOOP-4397:
-----------------------------------------

Hey Pete,

I didn't protect all writes to the dfs context because I only had time to look at the one case - no reason other than that, probably needs to be done.

Brian

> fuse-dfs causes corruptions on multi-threaded access
> ----------------------------------------------------
>
>                 Key: HADOOP-4397
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4397
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: contrib/fuse-dfs
>    Affects Versions: 0.18.1
>            Reporter: Brian Bockelman
>             Fix For: 0.18.2
>
>         Attachments: hadoop-4397.patch
>
>
> If multiple threads in the same process perform file system reads, then fuse-dfs causes various problems due to the per-context buffer.  I've seen this reflected in segmentation violations and corruptions.
> I'll attach a proposed patch which takes the "easy way" out - I surround all calls to dfs_read with a mutex.  You will obviously get performance degradations through thrashing if the threads are reading different parts of the file (but for our application, the multi-threaded reads are very, very infrequent.
> If we want to have fuse-dfs writes/reads in 0.19 or 0.20, we'll probably need to do the same thing with writes.
> This patch could be easily integrated as stands, or a more elaborate approach could be taken - per-thread buffers maybe?
> Thanks as always for looking into this,
> Brian

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