hadoop-mapreduce-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Lin Ma <lin...@gmail.com>
Subject Re: backup node question
Date Sun, 07 Apr 2013 07:51:28 GMT
Thanks Harsh,

For your comments, "What it means is that the NameNode need not store
anything locally", you mean Primary Name Node do not need to store
checkpoint/journal locally, and only need to keep memory image up-to-date
for edits?

regards,
Lin

On Sun, Apr 7, 2013 at 3:31 PM, Harsh J <harsh@cloudera.com> wrote:

> Hi Lin,
>
> My reply inline.
>
> On Sun, Apr 7, 2013 at 12:36 PM, Lin Ma <linlma@gmail.com> wrote:
> > Hi guys,
> >
> > I am reading from this paper to learn about backup nodes
> > (http://www.storageconference.org/2010/Papers/MSST/Shvachko.pdf),
> >
> > It is mentioned, "It contains all file system metadata information except
> > for block locations. It can perform all operations of the regular
> NameNode
> > that do not involve modification of the namespace or knowledge of block
> > locations. ", what kinds of operations do not need knowledge of block
> > locations?
>
> Operations that do not involve data reads or writes would not require
> knowledge of block locations. Applying also the restriction of no
> namespace mutation, an example would be listing directories and
> looking up file information via FileStatus objects (perhaps the only
> examples - its like a safemode but no reads either).
>
> > It is also mentioned, "Use of a BackupNode provides the option of running
> > the NameNode without persistent storage, delegating responsibility for
> the
> > namespace state persisting to the BackupNode.", what means "running the
> > NameNode without persistent storage" and "delegating responsibility for
> the
> > namespace state persisting"?
>
> What it means is that the NameNode need not store anything locally,
> but can rely on the edits being stored at the BackupNameNode which
> would continuously be receiving it. When restarted, it can grab a
> current checkpoint from the BNN and boot up anywhere, since there's no
> local storage requirement.
>
> --
> Harsh J
>

Mime
View raw message