Also, thinking about it more….. There are constant write loads where if the cluster is big enough compared to the write load that the flushes are not happening that often causing a profile like that to be cpu bound.
In my mind it really is about what configuration you have. If I have a high write load and I increase my cluster size 10 fold, it may be the case that I am limited by CPU as the memtable flushes are not happening as often since writes are thinned out across the cluster. Dean On 7/23/13 12:12 PM, "Hiller, Dean" <dean.hil...@nrel.gov> wrote: >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 <al...@datastax.com<mailto:al...@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-u...@incubator.apache.org<mailto:cassandra-user@incubator.apach >e.org>" ><cassandra-u...@incubator.apache.org<mailto:cassandra-user@incubator.apach >e.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 ><haj...@purdue.edu<mailto:haj...@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?? > > > >-- >View this message in context: >http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Are-Write >s-disk-bound-rather-than-CPU-bound-tp7589191.html >Sent from the [hidden >email]<http://user/SendEmail.jtp?type=node&node=7589236&i=1> mailing list >archive at Nabble.com<http://Nabble.com>. > > > >________________________________ >If you reply to this email, your message will be added to the discussion >below: >http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Are-Write >s-disk-bound-rather-than-CPU-bound-tp7589191p7589236.html >To unsubscribe from Are Writes disk-bound rather than CPU-bound?, click >here. >NAML<http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/temp >late/NamlServlet.jtp?macro=macro_viewer&id=instant_html%21nabble%3Aemail.n >aml&base=nabble.naml.namespaces.BasicNamespace-nabble.view.web.template.Na >bbleNamespace-nabble.view.web.template.NodeNamespace&breadcrumbs=notify_su >bscribers%21nabble%3Aemail.naml-instant_emails%21nabble%3Aemail.naml-send_ >instant_email%21nabble%3Aemail.naml> > > > >-- >Mohammad Hajjat >Ph.D. Student >Electrical and Computer Engineering >Purdue University > >________________________________ >View this message in context: Re: Are Writes disk-bound rather than >CPU-bound?<http://cassandra-user-incubator-apache-org.3065146.n2.nabble.co >m/Are-Writes-disk-bound-rather-than-CPU-bound-tp7589191p7589248.html> > >Sent from the cassandra-u...@incubator.apache.org mailing list >archive<http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/> > at Nabble.com. > > > >-- > >:- a) > > >Alex Popescu >@al3xandru
