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From "Allen, Jonathan" <jonathan.all...@hp.com>
Subject RE: Name Node Corruption When Shutdown Too Soon
Date Tue, 09 Feb 2010 20:05:00 GMT
Todd,

Unfortunately my test system is air gapped away from the internet so I haven't been able to
transfer my test case across yet but the basic steps as are follows:

1) start-dfs (also shutdown the secondary to make sure that it didn't checkpoint away the
edit log)
2) create lots of small files so that there is a large edit log (I created about 4,500 files
resulting in an edit log of just over 1MB).
3) stop-dfs
4) start-dfs
5) wait for name node to start reading the edit log but not long enough for it to finish reading
it (I waited for a couple of seconds).
6) stop-dfs
7) start-dfs
8) listing the hdfs directory now shows it in the same state as at step (1) rather than the
correct state as at step (3). 

This was running with the Yahoo distro of 0.20.1.

The dfs.name.dir is configured to use directories on 2 local drives and 1 NFS mounted drive.

Thanks,
Jonathan

Jonathan Allen
UKGP, NS&R, Defence and Security
HP Enterprise Services
Telephone +44 1682 292101
Email jonathan.allen.uk@hp.com
Street address, Unit 29, Alexandra Way, Ashchurch Business Park, Tewkesbury, Gloucestershire.
GL20 8NB

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-----Original Message-----
From: Todd Lipcon [mailto:todd@cloudera.com] 
Sent: 09 February 2010 01:11
To: hdfs-dev@hadoop.apache.org
Subject: Re: Name Node Corruption When Shutdown Too Soon

Hi Jonathan,

Another question: how have you configured dfs.name.dir? Do you have
several directories configured?

Thanks
-Todd

On Mon, Feb 8, 2010 at 4:45 PM, Todd Lipcon <todd@cloudera.com> wrote:
> Hey Jonathan,
>
> As Konstantin mentioned, I've been looking into a couple issues that
> could be related. At first glance it doesn't sound like you've run
> into quite the same thing.
>
> What version did you see this on? The steps to reproduce are something like:
>
> 1) Start a NN
> 2) Perform a bunch of edits so there is a large edit log
> 3) kill -9 the NN
> 4) start the NN again
> 5) while it is in the middle of replaying edits, kill -9 it again
> 6) start the NN, and lose all the previous edits?
>
> Or did I misunderstand what happened? If that sounds right, I'll give
> it a go and see if I can reproduce.
>
> Thanks
> -Todd
>
> On Sun, Feb 7, 2010 at 8:45 AM, Allen, Jonathan <jonathan.allen2@hp.com> wrote:
>> I've come across a name node bug and just wanted to check if it's a known issue before
I formally raise it (I've had a quick look through the database but couldn't see anything
obvious).
>>
>> If the name node is shut down before it has completed reading through the edit log
then the edit log gets removed without the image file being updated.  This results in name
node reverting to its previously saved state (out of sync with the data nodes) and the most
recent edits getting lost.
>>
>> Does anybody recognise this as a known issue or should I raise it?
>>
>> Thanks,
>> Jonathan Allen
>> UKGP, NS&R, Defence and Security
>> HP Enterprise Services
>> Telephone +44 1682 292101
>> Email jonathan.allen.uk@hp.com
>> Street address, Unit 29, Alexandra Way, Ashchurch Business Park, Tewkesbury, Gloucestershire.
GL20 8NB
>>
>> Hewlett-Packard Limited registered Office: Cain Road, Bracknell, Berks RG12 1HN
>> Registered No: 690597 England
>> The contents of this message and any attachments to it are confidential and may be
legally privileged. If you have received this message in error, you should delete it from
your system immediately and advise the sender.
>> To any recipient of this message within HP, unless otherwise stated you should consider
this message and attachments as "HP CONFIDENTIAL".
>>
>>
>>
>>
>

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