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From aaron morton <aa...@thelastpickle.com>
Subject Re: CPU Bound Writes
Date Sun, 21 Jul 2013 20:57:04 GMT
> 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


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