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From "Koji Noguchi" <knogu...@yahoo-inc.com>
Subject RE: Setting up another machine as secondary node
Date Thu, 14 May 2009 17:42:59 GMT
Before 0.19, fsimage/edits were on the same directory.
So whenever secondary finishes checkpointing, it copies back the fsimage
while namenode still kept on writing to the edits file.

Usually we observed some latency on the namenode side during that time.

HADOOP-3948 would probably help after 0.19 or later.

Koji

-----Original Message-----
From: Brian Bockelman [mailto:bbockelm@cse.unl.edu] 
Sent: Thursday, May 14, 2009 10:32 AM
To: core-user@hadoop.apache.org
Subject: Re: Setting up another machine as secondary node

Hey Koji,

It's an expensive operation - for the secondary namenode, not the  
namenode itself, right?  I don't particularly care if I stress out a  
dedicated node that doesn't have to respond to queries ;)

Locally we checkpoint+backup fairly frequently (not 5 minutes ...  
maybe less than the default hour) due to sheer paranoia of losing  
metadata.

Brian

On May 14, 2009, at 12:25 PM, Koji Noguchi wrote:

>> The secondary namenode takes a snapshot
>> at 5 minute (configurable) intervals,
>>
> This is a bit too aggressive.
> Checkpointing is still an expensive operation.
> I'd say every hour or even every day.
>
> Isn't the default 3600 seconds?
>
> Koji
>
> -----Original Message-----
> From: jason hadoop [mailto:jason.hadoop@gmail.com]
> Sent: Thursday, May 14, 2009 7:46 AM
> To: core-user@hadoop.apache.org
> Subject: Re: Setting up another machine as secondary node
>
> any machine put in the conf/masters file becomes a secondary namenode.
>
> At some point there was confusion on the safety of more than one
> machine,
> which I believe was settled, as many are safe.
>
> The secondary namenode takes a snapshot at 5 minute (configurable)
> intervals, rebuilds the fsimage and sends that back to the namenode.
> There is some performance advantage of having it on the local machine,
> and
> some safety advantage of having it on an alternate machine.
> Could someone who remembers speak up on the single vrs multiple
> secondary
> namenodes?
>
>
> On Thu, May 14, 2009 at 6:07 AM, David Ritch <david.ritch@gmail.com>
> wrote:
>
>> First of all, the secondary namenode is not a what you might think a
>> secondary is - it's not failover device.  It does make a copy of the
>> filesystem metadata periodically, and it integrates the edits into  
>> the
>> image.  It does *not* provide failover.
>>
>> Second, you specify its IP address in hadoop-site.xml.  This is where
> you
>> can override the defaults set in hadoop-default.xml.
>>
>> dbr
>>
>> On Thu, May 14, 2009 at 9:03 AM, Rakhi Khatwani
> <rakhi.khatwani@gmail.com
>>> wrote:
>>
>>> Hi,
>>>    I wanna set up a cluster of 5 nodes in such a way that
>>> node1 - master
>>> node2 - secondary namenode
>>> node3 - slave
>>> node4 - slave
>>> node5 - slave
>>>
>>>
>>> How do we go about that?
>>> there is no property in hadoop-env where i can set the ip-address
> for
>>> secondary name node.
>>>
>>> if i set node-1 and node-2 in masters, and when we start dfs, in
> both the
>>> m/cs, the namenode n secondary namenode processes r present. but i
> think
>>> only node1 is active.
>>> n my namenode fail over operation fails.
>>>
>>> ny suggesstions?
>>>
>>> Regards,
>>> Rakhi
>>>
>>
>
>
>
> -- 
> Alpha Chapters of my book on Hadoop are available
> http://www.apress.com/book/view/9781430219422
> www.prohadoopbook.com a community for Hadoop Professionals


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