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From Mohammad Hajjat <haj...@purdue.edu>
Subject Re: CPU Bound Writes
Date Sat, 20 Jul 2013 16:27:02 GMT
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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