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From "Hiller, Dean" <Dean.Hil...@nrel.gov>
Subject Re: Are Writes disk-bound rather than CPU-bound?
Date Tue, 23 Jul 2013 18:12:22 GMT
Out of curiosity, isn't what is really happening is this

"As writes keep coming in, memory fills up causing flushes to the commit log disk of the whole
memtable.  In a bursting scenario, writes are thus limited only by memory and cpu in short
bursting cases that tend to fit in memory.  In a more long window of constant writes, the
writes become limited by the constant flushing to disk of the memtable"

Ie. We kind of have two scenarios in my mind if I got that right that is from my understanding
that cassandra is write to memory first and asynchronously write to disk.

Later,
Dean

From: Alex Popescu <alexp@datastax.com<mailto:alexp@datastax.com>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Date: Tuesday, July 23, 2013 12:07 PM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Cc: "cassandra-user@incubator.apache.org<mailto:cassandra-user@incubator.apache.org>"
<cassandra-user@incubator.apache.org<mailto:cassandra-user@incubator.apache.org>>
Subject: Re: Are Writes disk-bound rather than CPU-bound?

I see pretty much the same formulation in the 1.2 docs, so I'm wondering what would be the
best rewrite of that paragraph?


On Tue, Jul 23, 2013 at 9:00 AM, hajjat <hajjat@purdue.edu<mailto:hajjat@purdue.edu>>
wrote:


On Tue, Jul 23, 2013 at 5:05 AM, aaron morton [via [hidden email]<http://user/SendEmail.jtp?type=node&node=7589248&i=0>]
<[hidden email]<http://user/SendEmail.jtp?type=node&node=7589248&i=1>>
wrote:
“/Insert-heavy workloads will actually be CPU-bound in Cassandra before being
memory-bound/”
What is the source for that ?

http://www.datastax.com/docs/0.8/cluster_architecture/cluster_planning
​​

This is because everything is
*first *written to the commit log *on disk*. Any thoughts??
Pretty much.

Cheers

-----------------
Aaron Morton
Cassandra Consultant
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 22/07/2013, at 8:58 AM, hajjat <[hidden email]<http://user/SendEmail.jtp?type=node&node=7589236&i=0>>
wrote:

“/Insert-heavy workloads will actually be CPU-bound in Cassandra before being
memory-bound/”

However, from reading the documentation
(http://www.datastax.com/docs/1.2/dml/about_writes) it seems the disk is the
real bottleneck in Writes rather than the CPU. This is because everything is
*first *written to the commit log *on disk*. Any thoughts??



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

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:- a)


Alex Popescu
@al3xandru
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