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From Mohammad Hajjat <haj...@purdue.edu>
Subject Re: CPU Bound Writes
Date Sun, 21 Jul 2013 21:00:25 GMT
Aaron, here is the source:
http://www.datastax.com/docs/0.8/cluster_architecture/cluster_planning

Thanks!


On Sun, Jul 21, 2013 at 4:57 PM, aaron morton <aaron@thelastpickle.com>wrote:

> > Wouldn't this make Writes disk-bound then? I think the documentation may
> have been a bit misleading then "Insert-heavy workloads will actually be
> CPU-bound in Cassandra before being memory-bound"?
> What is the source of the quote ?
>
> Cheers
> -----------------
> Aaron Morton
> Cassandra Consultant
> New Zealand
>
> @aaronmorton
> http://www.thelastpickle.com
>
> On 21/07/2013, at 4:27 AM, Mohammad Hajjat <hajjat@purdue.edu> wrote:
>
> > Thanks/Shukran, Jon! :)
> >
> > Wouldn't this make Writes disk-bound then? I think the documentation may
> have been a bit misleading then "Insert-heavy workloads will actually be
> CPU-bound in Cassandra before being memory-bound"?
> >
> >
> >
> >
> > On Sat, Jul 20, 2013 at 12:12 PM, Jonathan Haddad <
> jonathan.haddad@gmail.com> wrote:
> > Everything is written to the commit log. In the case of a crash,
> cassandra recovers by replaying the log.
> >
> >
> > On Sat, Jul 20, 2013 at 9:03 AM, Mohammad Hajjat <hajjat@purdue.edu>
> wrote:
> > Patricia,
> >
> > Thanks for the info. So are you saying that the *whole* data is being
> written on disk in the commit log, not just some sort of a summary/digest?
> > I'm writing 10MB objects and I'm noticing high latency (250 milliseconds
> even with ANY consistency), so I guess that explains my high delays?
> >
> > Thanks,
> > Mohammad
> >
> >
> > On Fri, Jul 19, 2013 at 2:17 PM, Patricia Gorla <
> gorla.patricia@gmail.com> wrote:
> > Kanwar,
> >
> > This is because writes are appends to the commit log, which is stored on
> disk, not memory. The commit log is then flushed to the memtable (in
> memory), before being written to an sstable on disk.
> >
> > So, most of the actions in sending out a write are writing to disk.
> >
> > Also see: http://www.datastax.com/docs/1.2/dml/about_writes
> >
> > Patricia
> >
> >
> > On Fri, Jul 19, 2013 at 1:05 PM, Kanwar Sangha <kanwar@mavenir.com>
> wrote:
> > “Insert-heavy workloads will actually be CPU-bound in Cassandra before
> being memory-bound”
> >
> >
> >
> > Can someone explain why the internals of why writes are CPU bound ?
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > --
> > Mohammad Hajjat
> > Ph.D. Student
> > Electrical and Computer Engineering
> > Purdue University
> >
> >
> >
> >
> > --
> > Mohammad Hajjat
> > Ph.D. Student
> > Electrical and Computer Engineering
> > Purdue University
>
>


-- 
*Mohammad Hajjat*
*Ph.D. Student*
*Electrical and Computer Engineering*
*Purdue University*

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