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From suresh srinivas <srini30...@gmail.com>
Subject Re: [Discuss] Merge federation branch HDFS-1052 into trunk
Date Wed, 27 Apr 2011 21:36:08 GMT
I ran these tests on my laptop. I would like to use this data to emphasize
that there is no regression in performance. I am not sure with just the
tests that I ran we could conclude there is a huge gain in performance with
federation. When out performance test team runs tests at scale we will get
more clearer picture.



On Wed, Apr 27, 2011 at 10:41 AM, Konstantin Boudnik <cos@boudnik.org>wrote:

> Interesting... while the read performance has only marginally improved
> <4% (still a good thing) the write performance shows significantly
> better improvements >10%. Very interesting asymmetry, indeed.
>
> Suresh, what was the size of the cluster in the testing?
>  Cos
>
> On Wed, Apr 27, 2011 at 10:02, suresh srinivas <srini30005@gmail.com>
> wrote:
> > I posted the TestDFSIO comparison with and without federation to
> HDFS-1052.
> > Please let me know if it addresses your concern. I am also adding it
> here:
> >
> > TestDFSIO read tests
> > *Without federation:*
> > ----- TestDFSIO ----- : read
> >           Date & time: Wed Apr 27 02:04:24 PDT 2011
> >       Number of files: 1000
> > Total MBytes processed: 30000.0
> >     Throughput mb/sec: 43.62329251162561
> > Average IO rate mb/sec: 44.619869232177734
> >  IO rate std deviation: 5.060306158158443
> >    Test exec time sec: 959.943
> >
> > *With federation:*
> > ----- TestDFSIO ----- : read
> >           Date & time: Wed Apr 27 02:43:10 PDT 2011
> >       Number of files: 1000
> > Total MBytes processed: 30000.0
> >     Throughput mb/sec: 45.657513857055456
> > Average IO rate mb/sec: 46.72107696533203
> >  IO rate std deviation: 5.455125923399539
> >    Test exec time sec: 924.922
> >
> > TestDFSIO write tests
> > *Without federation:*
> > ----- TestDFSIO ----- : write
> >           Date & time: Wed Apr 27 01:47:50 PDT 2011
> >       Number of files: 1000
> > Total MBytes processed: 30000.0
> >     Throughput mb/sec: 35.940755259031015
> > Average IO rate mb/sec: 38.236236572265625
> >  IO rate std deviation: 5.929484960036511
> >    Test exec time sec: 1266.624
> >
> > *With federation:*
> > ----- TestDFSIO ----- : write
> >           Date & time: Wed Apr 27 02:27:12 PDT 2011
> >       Number of files: 1000
> > Total MBytes processed: 30000.0
> >     Throughput mb/sec: 42.17884674597227
> > Average IO rate mb/sec: 43.11423873901367
> >  IO rate std deviation: 5.357057259968647
> >    Test exec time sec: 1135.298
> > {noformat}
> >
> >
> > On Tue, Apr 26, 2011 at 11:55 PM, suresh srinivas <srini30005@gmail.com
> >wrote:
> >
> >> Konstantin,
> >>
> >> Could you provide me link to how this was done on a big feature, like
> say
> >> append and how benchmark info was captured? I am planning to run dfsio
> >> tests, btw.
> >>
> >> Regards,
> >> Suresh
> >>
> >>
> >> On Tue, Apr 26, 2011 at 11:34 PM, suresh srinivas <srini30005@gmail.com
> >wrote:
> >>
> >>> Konstantin,
> >>>
> >>> On Tue, Apr 26, 2011 at 10:26 PM, Konstantin Shvachko <
> >>> shv.hadoop@gmail.com> wrote:
> >>>
> >>>> Suresh, Sanjay.
> >>>>
> >>>> 1. I asked for benchmarks many times over the course of different
> >>>> discussions on the topic.
> >>>> I don't see any numbers attached to jira, and I was getting the same
> >>>> response,
> >>>> Doug just got from you, guys: which is "why would the performance be
> >>>> worse".
> >>>> And this is not an argument for me.
> >>>>
> >>>
> >>> We had done testing earlier and had found that performance had not
> >>> degraded. We are waiting for out performance team to publish the
> official
> >>> numbers to post it to the jira. Unfortunately they are busy qualifying
> 2xx
> >>> releases currently. I will get the perf numbers and post them.
> >>>
> >>>
> >>>>
> >>>> 2. I assume that merging requires a vote. I am sure people who know
> >>>> bylaws
> >>>> better than I do will correct me if it is not true.
> >>>> Did I miss the vote?
> >>>>
> >>>
> >>>
> >>> As regards to voting, since I was not sure about the procedure, I had
> >>> consulted Owen about it. He had indicated that voting is not necessary.
> If
> >>> the right procedure is to call for voting, I will do so. Owen any
> comments?
> >>>
> >>>
> >>>>
> >>>> It feels like you are rushing this and are not doing what you would
> >>>> expect
> >>>> others to
> >>>> do in the same position, and what has been done in the past for such
> >>>> large
> >>>> projects.
> >>>>
> >>>
> >>> I am not trying to rush here and not follow the procedure required. I
> am
> >>> not sure about what the procedure is. Any pointers to it is
> appreciated.
> >>>
> >>>
> >>>>
> >>>> Thanks,
> >>>> --Konstantin
> >>>>
> >>>>
> >>>> On Tue, Apr 26, 2011 at 9:43 PM, Doug Cutting <cutting@apache.org>
> >>>> wrote:
> >>>>
> >>>> > Suresh, Sanjay,
> >>>> >
> >>>> > Thank you very much for addressing my questions.
> >>>> >
> >>>> > Cheers,
> >>>> >
> >>>> > Doug
> >>>> >
> >>>> > On 04/26/2011 10:29 AM, suresh srinivas wrote:
> >>>> > > Doug,
> >>>> > >
> >>>> > >
> >>>> > >> 1. Can you please describe the significant advantages
this
> approach
> >>>> has
> >>>> > >> over a symlink-based approach?
> >>>> > >
> >>>> > > Federation is complementary with symlink approach. You could
> choose
> >>>> to
> >>>> > > provide integrated namespace using symlinks. However, client
side
> >>>> mount
> >>>> > > tables seems a better approach for many reasons:
> >>>> > > # Unlike symbolic links, client side mount tables can choose
to go
> to
> >>>> > right
> >>>> > > namenode based on configuration. This avoids unnecessary RPCs
to
> the
> >>>> > > namenodes to discover the targer of symlink.
> >>>> > > # The unavailability of a namenode where a symbolic link is
> >>>> configured
> >>>> > does
> >>>> > > not affect reaching the symlink target.
> >>>> > > # Symbolic links need not be configured on every namenode
in the
> >>>> cluster
> >>>> > and
> >>>> > > future changes to symlinks need not be propagated to multiple
> >>>> namenodes.
> >>>> > In
> >>>> > > client side mount tables, this information is in a central
> >>>> configuration.
> >>>> > >
> >>>> > > If a deployment still wants to use symbolic link, federation
does
> not
> >>>> > > preclude it.
> >>>> > >
> >>>> > >> It seems to me that one could run multiple namenodes on
separate
> >>>> boxes
> >>>> > > and run multile datanode processes per storage box
> >>>> > >
> >>>> > > There are several advantages to using a single datanode:
> >>>> > > # When you have large number of namenodes (say 20), the cost
of
> >>>> running
> >>>> > > separate datanodes in terms of process resources such as memory
is
> >>>> huge.
> >>>> > > # The disk i/o management and storage utilization using a
single
> >>>> datanode
> >>>> > is
> >>>> > > much better, as it has complete view the storage.
> >>>> > > # In the approach you are proposing, you have several clusters
to
> >>>> manage.
> >>>> > > However with federation, all datanodes are in a single cluster;
> with
> >>>> > single
> >>>> > > configuration and operationally easier to manage.
> >>>> > >
> >>>> > >> The patch modifies much of the logic of Hadoop's central
> component,
> >>>> upon
> >>>> > > which the performance and reliability of most other components
of
> the
> >>>> > > ecosystem depend.
> >>>> > > That is not true.
> >>>> > >
> >>>> > > # Namenode is mostly unchanged in this feature.
> >>>> > > # Read/write pipelines are unchanged.
> >>>> > > # The changes are mainly in datanode:
> >>>> > > #* the storage, FSDataset, Directory and Disk scanners now
have
> >>>> another
> >>>> > > level to incorporate block pool ID into the hierarchy. This
is not
> a
> >>>> > > significant change that should cause performance or stability
> >>>> concerns.
> >>>> > > #* datanodes use a separate thread per NN, just like the existing
> >>>> thread
> >>>> > > that communicates with NN.
> >>>> > >
> >>>> > >> Can you please tell me how this has been tested beyond
unit
> tests?
> >>>> > > As regards to testing, we have passed 600+ tests. In hadoop,
these
> >>>>  tests
> >>>> > > are mostly integration tests and not pure unit tests.
> >>>> > >
> >>>> > > While these tests have been extensive, we have also been testing
> this
> >>>> > branch
> >>>> > > for last 4 months, with QA validation that reflects our production
> >>>> > > environment. We have found the system to be stable, performing
> well
> >>>> and
> >>>> > have
> >>>> > > not found any blockers with the branch so far.
> >>>> > >
> >>>> > > HDFS-1052 has been open more than a year now. I had also sent
an
> >>>> email
> >>>> > about
> >>>> > > this merge around 2 months ago. There are 90 subtasks that
have
> been
> >>>> > worked
> >>>> > > on last couple of months under HDFS-1052. Given that there
was
> enough
> >>>> > time
> >>>> > > to ask these questions, your email a day before I am planning
to
> >>>> merge
> >>>> > the
> >>>> > > branch into trunk seems late!
> >>>> > >
> >>>> >
> >>>>
> >>>
> >>>
> >>>
> >>> --
> >>> Regards,
> >>> Suresh
> >>>
> >>>
> >>
> >>
> >> --
> >> Regards,
> >> Suresh
> >>
> >>
> >
> >
> > --
> > Regards,
> > Suresh
> >
>



-- 
Regards,
Suresh

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