The write and read load is very minimal the moment. Roughly 10 writes + 10 reads / second. So 20 operations per second. Don't think that overloads my cluster, does it?
2012/1/5 Philippe <watche...@gmail.com> > You may be overloading the cluster though... > > My hypothesis is that your traffic is being spread across your node and > that one slow node is slowing down the fraction of traffic that goes to > that node (when it's acting as coordinator). > So what I would do is reduce the read load a lot to make sure I don't > overload the cluster and measure if I see a 1/RF improvement in response > time which would validate my hypothesis. > > > 2012/1/5 R. Verlangen <ro...@us2.nl> > > It does not appear to affect the response time, certainly not in a >> positive way. >> >> >> 2012/1/5 Philippe <watche...@gmail.com> >> >>> What if you shutdown the cassandra service on the slow node, does that >>> improve your read performance ? >>> If it does then that sole node is responsible for the slow down because >>> it can't act as a coordinator fast enough. >>> >>> 2012/1/5 R. Verlangen <ro...@us2.nl> >>> >>> I'm also reading with CL = ONE >>>> >>>> >>>> 2012/1/5 Philippe <watche...@gmail.com> >>>> >>>>> Depending on the CL you're reading at it will yes : if the CL requires >>>>> that the "slow" node create a digest of the data and send it to the >>>>> coordinator then it might explain the poor performance on reads. What is >>>>> your read CL ? >>>>> >>>>> 2012/1/5 R. Verlangen <ro...@us2.nl> >>>>> >>>>> As I posted this I noticed that the other node's CPU is running high >>>>>> on some other cronjobs (every couple of minutes to 60% usage). Is the >>>>>> lack >>>>>> of more CPU cycles a problem in this case? >>>>>> >>>>>> Robin >>>>>> >>>>>> 2012/1/5 R. Verlangen <ro...@us2.nl> >>>>>> >>>>>> CPU is idle (< 10% usage). Disk reads occasionally blocks over >>>>>>> 32/64K. Writes around 0-5MB per second. Network traffic 0.1 / 0.1 MB/s >>>>>>> (in >>>>>>> / out). Paging 0. System int ~ 1300, csw ~ 2500. >>>>>>> >>>>>>> >>>>>>> 2012/1/5 Philippe <watche...@gmail.com> >>>>>>> >>>>>>>> What can you see in vmstat/dstat ? >>>>>>>> Le 5 janv. 2012 11:58, "R. Verlangen" <ro...@us2.nl> a écrit : >>>>>>>> >>>>>>>> Hi there, >>>>>>>>> >>>>>>>>> I'm running a cassandra 0.8.6 cluster with 2 nodes (in 2 DC's), RF >>>>>>>>> = 2. Actual data on the nodes is only 1GB. Disk latency < 1ms. Disk >>>>>>>>> throughput ~ 0.4MB/s. OS load always below 1 (on a 8 core machine >>>>>>>>> with 16GB >>>>>>>>> ram). >>>>>>>>> >>>>>>>>> When I'm running my writes against the cluster with cl = ONE all >>>>>>>>> reads appear to be faster then the writes. >>>>>>>>> >>>>>>>>> Average write speed = 1600us/operation >>>>>>>>> Average read speed = 200us/operation >>>>>>>>> >>>>>>>>> I'm really wondering why this is the case. Anyone got a clue? >>>>>>>>> >>>>>>>>> With kind regards, >>>>>>>>> Robin >>>>>>>>> >>>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>> >> >
