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Date: Wed, 23 Dec 2009 18:38:13 -0800
Message-ID: <314098690912231838r4126d609j1d345a34c3217b23@mail.gmail.com>
Subject: Re: Secondary NameNodes or NFS exports?
From: Jason Venner <jason.hadoop@gmail.com>
To: common-user@hadoop.apache.org
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I agree, it seems very wrong, that is why I need a block of time to really
verify the behavior.

My test case is the following, and the same test fails in 18.3 and 19.0 and
19.1

set up a single node cluster, 1 namenode, 1 datanode, 1 secondary, all on
the same machine.
set the checkpoint interval to 2 minutes (120 sec)

make a few files, wait, and verify that a checkpoint can happen.

recursively start coping a deep tree into hdfs, what the checkpoint fail
with a timestamp error.

The code explicitly uses the edits.new for the checkpoint verification
timestamp.

The window is the time from the take of the edit log to the return of the
fsimage.

On Wed, Dec 23, 2009 at 5:52 PM, Brian Bockelman <bbockelm@cse.unl.edu>wrote:

> Hey Jason,
>
> This analysis seems fairly unlikely - are you claiming that no edits can be
> merged if files are being created?  Isn't this what edits.new is for?
>
> We roll the edits log successfully during periods of high transfer, when a
> new file is being created every 1 second or so.
>
> We have had issues with unmergeable edits before - there might be some race
> conditions in this area.
>
> Brian
>
> On Dec 23, 2009, at 7:07 PM, Jason Venner wrote:
>
> > I have no current solution.
> > When I can block a few days, I am going to instrument the code a bit more
> to
> > verify my understanding.
> >
> > I believe the issue is that the time stamp is being checked against the
> > active edit log (the new one created then the checkpoint started) rather
> > than the time stamp of the rolled (old) edit log.
> > As long as no transactions have hit, the time stamps are the same.
> >
> >
> > On Wed, Dec 23, 2009 at 11:23 AM, Stas Oskin <stas.oskin@gmail.com>
> wrote:
> >
> >> Hi.
> >>
> >> What was your solution to this then?
> >>
> >> Regards.
> >>
> >> On Sat, Dec 5, 2009 at 7:43 AM, Jason Venner <jason.hadoop@gmail.com>
> >> wrote:
> >>
> >>> I have dug into this more, it turns out the problem is unrelated to nfs
> >> or
> >>> solaris.
> >>> The issue is that if there is a meta data change, while the secondary
> is
> >>> rebuilding the fsimage, the rebuilt image is rejected.
> >>> On our production cluster, there is almost never a moment where there
> is
> >>> not
> >>> a file being created or altered, and as such the secondary is never
> make
> >> a
> >>> fresh fsimage for the cluster.
> >>>
> >>> I have checked this with several hadoop variants and with vanilla
> >>> distributions with the namenode, secondary and a datanode all running
> on
> >>> the
> >>> same machine.
> >>>
> >>> On Tue, Oct 27, 2009 at 8:03 PM, Jason Venner <jason.hadoop@gmail.com
> >>>> wrote:
> >>>
> >>>> The namenode would never accept the rebuild fsimage from the
> secondary,
> >>> so
> >>>> the edit logs grew with outbounds.
> >>>>
> >>>>
> >>>> On Tue, Oct 27, 2009 at 10:51 AM, Stas Oskin <stas.oskin@gmail.com>
> >>> wrote:
> >>>>
> >>>>> Hi.
> >>>>>
> >>>>> You mean, you couldn't recover the NameNode from checkpoints because
> >> of
> >>>>> timestamps?
> >>>>>
> >>>>> Regards.
> >>>>>
> >>>>> On Tue, Oct 27, 2009 at 4:49 PM, Jason Venner <
> jason.hadoop@gmail.com
> >>>>>> wrote:
> >>>>>
> >>>>>> We have been having some trouble with the secondary on a cluster
> >> that
> >>>>> has
> >>>>>> one edit log partition on an nfs server, with the namenode rejecting
> >>> the
> >>>>>> merged images due to timestamp missmatches.
> >>>>>>
> >>>>>>
> >>>>>> On Mon, Oct 26, 2009 at 10:14 AM, Stas Oskin <stas.oskin@gmail.com>
> >>>>> wrote:
> >>>>>>
> >>>>>>> Hi.
> >>>>>>>
> >>>>>>> Thanks for the advice, it seems that the initial approach of
> >> having
> >>>>>> single
> >>>>>>> SecNameNode writing to exports is the way to go.
> >>>>>>>
> >>>>>>> By the way, I asked this already, but wanted to clarify:
> >>>>>>>
> >>>>>>> * It's possible to set how often SecNameNode checkpoints the data
> >>>>> (what
> >>>>>> is
> >>>>>>> the setting by the way)?
> >>>>>>>
> >>>>>>> * It's possible to let NameNode write to exports as well together
> >>> with
> >>>>>>> local
> >>>>>>> disk, which ensures the latest possible meta-data in case of disk
> >>>>> crash
> >>>>>>> (compared to pereodic check-pointing), but it's going to slow down
> >>> the
> >>>>>>> operations due to network read/writes.
> >>>>>>>
> >>>>>>> Thanks again.
> >>>>>>>
> >>>>>>> On Thu, Oct 22, 2009 at 10:03 PM, Patrick Angeles
> >>>>>>> <patrickangeles@gmail.com>wrote:
> >>>>>>>
> >>>>>>>> From what I understand, it's rather tricky to set up multiple
> >>>>> secondary
> >>>>>>>> namenodes. In either case, running multiple 2ndary NNs doesn't
> >> get
> >>>>> you
> >>>>>>>> much.
> >>>>>>>> See this thread:
> >>>>>>>>
> >>>>>
> http://www.mail-archive.com/core-user@hadoop.apache.org/msg06280.html
> >>>>>>>>
> >>>>>>>> On Wed, Oct 21, 2009 at 10:44 AM, Stas Oskin <
> >>> stas.oskin@gmail.com>
> >>>>>>> wrote:
> >>>>>>>>
> >>>>>>>>> To clarify, it's either let single SecNameNode to write to
> >>>>> multiple
> >>>>>> NFS
> >>>>>>>>> exports, or actually have multiple SecNameNodes.
> >>>>>>>>>
> >>>>>>>>> Thanks again.
> >>>>>>>>>
> >>>>>>>>> On Wed, Oct 21, 2009 at 4:43 PM, Stas Oskin <
> >>> stas.oskin@gmail.com
> >>>>>>
> >>>>>>>> wrote:
> >>>>>>>>>
> >>>>>>>>>> Hi.
> >>>>>>>>>>
> >>>>>>>>>> I'm want to keep a checkpoint data on several separate
> >>> machines
> >>>>> for
> >>>>>>>>> backup,
> >>>>>>>>>> and deliberating between exporting these machines disks via
> >>> NFS,
> >>>>> or
> >>>>>>>>> actually
> >>>>>>>>>> running Secondary Name Nodes there.
> >>>>>>>>>>
> >>>>>>>>>> Can anyone advice what would be better in my case?
> >>>>>>>>>>
> >>>>>>>>>> Regards.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> --
> >>>>>> Pro Hadoop, a book to guide you from beginner to hadoop mastery,
> >>>>>> http://www.amazon.com/dp/1430219424?tag=jewlerymall
> >>>>>> www.prohadoopbook.com a community for Hadoop Professionals
> >>>>>>
> >>>>>
> >>>>
> >>>>
> >>>>
> >>>> --
> >>>> Pro Hadoop, a book to guide you from beginner to hadoop mastery,
> >>>> http://www.amazon.com/dp/1430219424?tag=jewlerymall
> >>>> www.prohadoopbook.com a community for Hadoop Professionals
> >>>>
> >>>
> >>>
> >>>
> >>> --
> >>> Pro Hadoop, a book to guide you from beginner to hadoop mastery,
> >>> http://www.amazon.com/dp/1430219424?tag=jewlerymall
> >>> www.prohadoopbook.com a community for Hadoop Professionals
> >>>
> >>
> >
> >
> >
> > --
> > Pro Hadoop, a book to guide you from beginner to hadoop mastery,
> > http://www.amazon.com/dp/1430219424?tag=jewlerymall
> > www.prohadoopbook.com a community for Hadoop Professionals
>
>


-- 
Pro Hadoop, a book to guide you from beginner to hadoop mastery,
http://www.amazon.com/dp/1430219424?tag=jewlerymall
www.prohadoopbook.com a community for Hadoop Professionals

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