Hi Anoop, Thanks for the clarification.
So let's take one example. Let's say I have 4 nodes and a replication factor set to 3. I have a region hosted on N1, replicated on N2 and N3. Nothing about this region on N4. It's time to run a MR, and someone need to work on the given region. N1 is to busy, so region will be given to another node. Does it mean it will be given randomly between N2, N3 and N4? If it's given to N4, it's missing an oportunity to get the data almost locally. Also, if the job is given to N2 or N3, are they going to remotly query the data over the network from N1? Or are they able to ready it from the replicate? Based on what you are saying, seems that they will retrieve it for N1. Is there not another oportunity to improve the process by reading from the replicated data and not from the master one? When you are talking about "the short circuit read option", is this something we need to enable as a property? Or it's more like a piece of code? JM 2012/12/10, Anoop Sam John <[email protected]>: >>But if the job is running there, it can also be > considered as running locally, right? Or will it always be retrieved > from the datanode linked to the RS hosting the region we are dealing > with? Not sure I'm clear :( > > Hi Jean, > Sorry I have not seen the history of this mailing thread. > As far as seeing this question from you, I guess the MR is scanning HTable > data, even if the job is running on a replicate I dont think it will be > local. The MR job need to fetch the data via HBase only. Means it need to > contact the RS hosting the region. Then in turn HBase will contact any of > the DN where the data is available. So it will be multiple steps. There is > nothing like one RS in some way linked to one DN. From which DN the data to > be fetched depends on the decision taken by the DFS client. May be it will > not contact any DN but will do a local read, if the short circuit read > option is enabled and the data is there in the same server where the region > is hosted.. I guess I make it clear here. :) > > -Anoop- > > ________________________________________ > From: Jean-Marc Spaggiari [[email protected]] > Sent: Monday, December 10, 2012 7:33 PM > To: [email protected] > Subject: Re: Heterogeneous cluster > > @Asaf & Robert: I have posted the code here. But be careful with it. > Read Mike's comment above. > http://www.spaggiari.org/index.php/hbase/changing-the-hbase-default-loadbalancer > I'm a newby on HBase, so you're better to rely on someone more > experienced feedback. > > @Mike: > > Hi Mike, > > I totally agree with your opinion. My balancer is totally a hack on a > 'Frankencluster' (BTW, I LOVE this description! Perfect fit!) and a > way for me to take a deeper look at HBase's code. > > One question about data locality. When you run an HBase MR, even with > a factor 3 replication, data is considered local only if it's running > on the RS version the region is stored. But does HBase has a way to > see if it can be run on any of the replicats? The replicate might be > on a different rack. But if the job is running there, it can also be > considered as running locally, right? Or will it always be retrieved > from the datanode linked to the RS hosting the region we are dealing > with? Not sure I'm clear :( > > JM > > 2012/12/9, Michael Segel <[email protected]>: >> Ok... >> >> From a production/commercial grade answer... >> >> With respect to HBase, you will have 1 live copy and 2 replications. >> (Assuming you didn't change this.) So when you run against HBase, data >> locality becomes less of an issue. >> And again, you have to temper that with that it depends on the number of >> regions within the table... >> >> A lot of people, including committers tend to get hung up on some of the >> details and they tend to lose focus on the larger picture. >> >> If you were running a production cluster and your one node was radically >> different... then you would be better off taking it out of the cluster >> and >> making it an edge node. (Edge nodes are very important...) >> >> If we're talking about a very large cluster which has evolved... then you >> would want to work out your rack aware placements. Note that rack aware >> is >> a logical and not a physical location. So you can modify it to let the >> distro's placement take the hint and move the data. This is more of a >> cheat >> and even here... I think that at scale, the potential improvement gains >> are >> going to be minimal. >> >> This works for everything but HBase. >> >> On that note, it doesn't matter. Again, assume that you have your data >> equally distributed around the cluster and that your access pattern is to >> all nodes in the cluster. The parallelization in the cluster will >> average >> out the slow ones. >> >> In terms of your small research clusters... >> >> You're not looking at performance when you build a 'Frankencluster' >> >> Specifically to your case... move all the data to that node and you end >> up >> with both a networking and disk i/o bottlenecks. >> >> You're worried about the noise. >> >> Having said that... >> >> If you want to improve the balancer code, sure, however, you're going to >> need to do some work where you capture your cluster's statistics so that >> the >> balancer has more intelligence. >> >> You may start off wanting to allow HBase to take hints about the cluster, >> but in truth, I don't think its a good idea. Note, I realize that you and >> Jean-Marc are not suggesting that it is your intent to add something like >> this, but that someone will create a JIRA and then someone else may act >> upon >> it.... >> >> IMHO, that's a lot of work, adding intelligence to the HBase Scheduler and >> I >> don't think it will really make a difference in terms of overall >> performance. >> >> >> Just saying... >> >> -Mike >> >> On Dec 8, 2012, at 5:50 PM, Robert Dyer <[email protected]> wrote: >> >>> I of course can not speak for Jean-Marc, however my use case is not very >>> corporate. It is a small cluster (9 nodes) and only 1 of those nodes is >>> different (drastically different). >>> >>> And yes, I configured it so that node has a lot more map slots. >>> However, >>> the problem is HBase balances without regard to that and thus even >>> though >>> more map tasks run on those nodes they are not data-local! If I have a >>> balancer that is able to keep more regions on that particular node, then >>> the data locality of my map tasks is improved. >>> >>> >>> On Sat, Dec 8, 2012 at 5:45 PM, Michael Segel >>> <[email protected]>wrote: >>> >>>> Take what I say with a grain of kosher salt. (Its what they put on your >>>> drink glasses because the grains are bigger. ;-) >>>> >>>> I think what you are doing is cool hack, however in the bigger picture, >>>> you shouldn't have to do this with your load balancer. Also it doesn't >>>> matter if you think about ti. >>>> >>>> With a heterogenous cluster, you will not share the same configuration >>>> across all machines in the cluster. You will change the number of slots >>>> per >>>> node based on its capacity. >>>> That will limit what amount of work could be done on the same cluster. >>>> >>>> You could also consider playing with the rack aware aspects of your >>>> cluster. >>>> You could make all of your 2CPU machines in the same rack. >>>> >>>> In theory... machine, rack , second rack is how the data is >>>> distributed. >>>> In theory if the 2CPU cores are neighbors, then the 2nd and or 3rd copy >>>> goes to another machine. >>>> >>>> Trying to write a custom balancer, may be a good hack, but not good in >>>> terms of corporate life. >>>> >>>> Just saying! >>>> >>>> -Mike >>>> >>>> On Dec 8, 2012, at 1:34 PM, Jean-Marc Spaggiari >>>> <[email protected]> >>>> wrote: >>>> >>>>> Hi, >>>>> >>>>> It's not yet available anywhere. I will post it today or tomorrow, >>>>> just the time to remove some hardcoding I did into it ;) It's a quick >>>>> and dirty PerformanceBalancer. It's not a CPULoadBalencer. >>>>> >>>>> Anyway, I will give more details over the week-end, but there is >>>>> absolutly nothing extraordinaire with it. >>>>> >>>>> JM >>>>> >>>>> 2012/12/8, Robert Dyer <[email protected]>: >>>>>> I too am interested in this custom load balancer, as I was actually >>>>>> just >>>>>> starting to look into writing one that does the same thing for >>>>>> my heterogeneous cluster! >>>>>> >>>>>> Is this available somewhere? >>>>>> >>>>>> On Sat, Dec 8, 2012 at 9:17 AM, James Chang <[email protected]> >>>>>> wrote: >>>>>> >>>>>>> By the way, I saw you mentioned that you >>>>>>> have built a "LoadBalancer", could you kindly >>>>>>> share some detailed info about it? >>>>>>> >>>>>>> Jean-Marc Spaggiari 於 2012年12月8日星期六寫道： >>>>>>> >>>>>>>> Hi, >>>>>>>> >>>>>>>> Here is the situation. >>>>>>>> >>>>>>>> I have an heterogeneous cluster with 2 cores CPUs, 4 cores CPUs and >>>>>>>> 8 >>>>>>>> cores CPUs servers. The performances of those different servers >>>>>>>> allow >>>>>>>> them to handle different size of load. So far, I built a >>>>>>>> LoadBalancer >>>>>>>> which balance the regions over those servers based on the >>>>>>>> performances. And it’s working quite well. The RowCounter went down >>>>>>>> from 11 minutes to 6 minutes. However, I can still see that the >>>>>>>> tasks >>>>>>>> are run on some servers accessing data on other servers, which >>>>>>>> overwhelme the bandwidth and slow done the process since some 2 >>>>>>>> cores >>>>>>>> servers are assigned to count some rows hosted on 8 cores servers. >>>>>>>> >>>>>>>> I’m looking for a way to “force” the tasks to run on the servers >>>>>>>> where >>>>>>>> the regions are assigned. >>>>>>>> >>>>>>>> I first tried to reject the tasks on the Mapper setup method when >>>>>>>> the >>>>>>>> data was not local to see if the tracker will assign it to another >>>>>>>> server. No. It’s just failing and mostly not re-assigned. I tried >>>>>>>> IOExceptions, RuntimeExceptions, InterruptionExceptions with no >>>>>>>> success. >>>>>>>> >>>>>>>> So now I have 3 possible options. >>>>>>>> >>>>>>>> The first one is to move from the MapReduce to the Coprocessor >>>>>>>> EndPoint. Running locally on the RegionServer, it’s accessing only >>>>>>>> the >>>>>>>> local data and I can manually reject all what is not local. >>>>>>>> Therefor >>>>>>>> it’s achieving my needs, but it’s not my preferred options since I >>>>>>>> would like to keep the MR features. >>>>>>>> >>>>>>>> The second option is to tell Hadoop where the tasks should be >>>>>>>> assigned. Should that be done by HBase? By Hadoop? I don’t know. >>>>>>>> Where? I don’t know either. I have started to look at JobTracker >>>>>>>> and >>>>>>>> JobInProgress code but it seems it will be a big task. Also, doing >>>>>>>> that will mean I will have to re-patch the distributed code each >>>>>>>> time >>>>>>>> I’m upgrading the version, and I will have to redo everything when >>>>>>>> I >>>>>>>> will move from 1.0.x to 2.x… >>>>>>>> >>>>>>>> Third option is to not process the task if the data is not local. I >>>>>>>> mean, on the map method, simply have a if (!local) return; right >>>>>>>> from >>>>>>>> the beginning and just do nothing. This will not work for things >>>>>>>> like >>>>>>>> RowCount since all the entries are required, but for some of my >>>>>>>> usecases this might work where I don’t necessary need all the data >>>>>>>> to >>>>>>>> be processed. I will not be efficient stlil the task will still >>>>>>>> scan >>>>>>>> the entire region. >>>>>>>> >>>>>>>> My preferred option is definitively the 2nd one, but it seems also >>>>>>>> to >>>>>>>> be the most difficult one. The Third one is very easy to implement. >>>>>>>> Need 2 lines to see if the data is local. But it’s not working for >>>>>>>> all >>>>>>>> the scenarios, and is more like a dirty fix. The coprocessor option >>>>>>>> might be doable too since I already have all the code for my >>>>>>>> MapReduce >>>>>>>> jobs. So it might be an acceptable option. >>>>>>>> >>>>>>>> I’m wondering if anyone already faced this situation and worked on >>>>>>>> something, and if not, do you have any other ideas/options to >>>>>>>> propose, >>>>>>>> or can someone point me to the right classes to look at to >>>>>>>> implement >>>>>>>> the solution 2? >>>>>>>> >>>>>>>> Thanks, >>>>>>>> >>>>>>>> JM >>>>>>>> >>>>>>> >>>>>> >>>>>> >>>>>> >>>>>> -- >>>>>> >>>>>> Robert Dyer >>>>>> [email protected] >>>>>> >>>>> >>>> >>>> >>> >>> >>> -- >>> >>> Robert Dyer >>> [email protected] >> >>
