Ditto, useful information! Thanks Daniel! W.R.T. commodity hardware: That really should be commodity servers. The 'gold standard' for Google when they wrote the Bigtable paper was two dual core Opteron processors with 8GB memory which is what we use on our 4 node test cluster.
--- Jim Kellerman, Senior Engineer; Powerset > -----Original Message----- > From: Bryan Duxbury [mailto:[EMAIL PROTECTED] > Sent: Wednesday, May 07, 2008 9:42 PM > To: [email protected] > Subject: Re: Advice for smaller clusters in write-heavy environments > > This is super useful information! Thanks for taking the time > to write it up. Maybe this should be transplanted onto the wiki? > > -Bryan > > On May 7, 2008, at 9:29 PM, Daniel Leffel wrote: > > > I thought I might share back with the users my experience > in getting > > HBase running on a small, 4 node cluster. I ran into a lot > of trouble > > in getting started, some because of bugs and some specific > to my use > > case. My learnings I think will hopefully be valuable to new users. > > > > First of all, let me compliment the amazing group of folks > developing > > HBase. > > Also, I'd like to say that we owe a lot to the amazing strategy > > Powerset has taken as a company to propel the development of their > > product, both leveraging and contributing to open source - what you > > guys are doing is nothing short than amazing! > > > > My basic use case is to persist a large (and growing) > sparce dataset > > and enable constant incremental re-computation. In order to test > > performance for this use case, it was important to load a > test initial > > dataset - roughly 220 million rows and 6 columns (for now, I'll say > > columns generically - I'll get it to strategy of column families). > > > > Some of my learnings > > > > - "Commodity Hardware" is relative. When I first heard > the term, I > > (and > > many others I know) considered this to be on the order of > > desktop-grade > > machines - the machines I'd purchased were Dual Core 2+ Ghz Dell > > Desktops > > (purchased on eBay for $350 a piece). Well, you can > definitely do > > certain > > tasks within the framework with these types of machines, but an > > ideal > > configuration consists of something much stronger - > server- grade, > > quad core, > > 8Gigs of RAM, etc. HBase (particularly if you are going > to do a lot > > of > > writes), needs really good Machine IO . If you are going > to try to > > use > > machines with slow drives and controllers, it might be > possible if > > you have > > a ton of datanodes, but not as advisable on smaller clusters. > > - Ideally, you should always insure that there is one processor > > available > > for the region server daemon and at least 2 processors for > > tasktracker (or 1 > > if you limit the map and reduce tasks to one each), if you are > > going to run > > heavy map/reduce jobs. The trouble with not doing so is > that until > > 0.2, when > > there will be better load balancing on regionservers, > it's always > > possible > > that a single region server can be called on to shoulder > the full > > load of > > all tasktrackers. If you have a large write operations > happening, > > you could > > otherwise cause splits and/or compaction to take too long > > (expensive > > operations) and cause your job to crawl to near halt if > your lucky, > > or die > > completely. This means, if you're only using dual core machines, > > I'd suggest > > that at least during heavy data-writing periods, you consider > > running either > > regionservers or tasktracker, but probably not both on the same > > machine. > > - All machines should run the datanode - this helps the > > regionservers to > > distribute the IO load better. That way, when an expensive > > operation like > > compaction starts, it's spread over more machines. Also, > Hadoop can > > localize > > frequently used files, to some degree. > > - Running bin/stop-hbase.sh can sometimes take a long time. > > Sometimes, > > regionservers are waiting for a lease to expire. There are a few > > times when > > there are dead processes (especially if you didn't take > the earlier > > suggestions) so check the logs (.out), but often you > just need to > > wait > > longer and it's worth it. > > - If you are writing from a MR job, it's most beneficial to find > > the > > right balance of number of tasks. Too many tasks means too many > > splits, > > startup and commits. Too few, and your region servers > don't get the > > benefit > > of a break (the time it takes to commit and initialize a new > > task) - not too > > mention less to repeat after a failure. > > - Use the new release candidate 0.1.2 #1. It has a > number of fixes > > in it > > that help for issues related to small clusters - I don't regard > > prior > > releases as usable for those of us being cheap about hardware. > > - Don't be afraid to adjust which daemons you run on which > > machines. For > > example, for my first large (initial) load, I shutdown all but a > > couple of > > tasktrackers and started up more region servers, whereas > in normal > > operation, that ratio will probably be flipped. > > - Watch the number of regions you have on any particular > > regionserver. > > I'm in the process at the moment of testing how far you can push > > this, but > > the big concern is OOME - and unless you're running the latest > > release > > candidate, you're going to have big problems after an OOME. > > > > > > Hope this is helpful, St^ack, please feel free to point out > where I'm > > wrong. > > :-) > > > > Danny > > > > > > PS. Thanks again to St^ack. He went over and above the call > of duty to > > help me and it's bought a ton of confidence I now have in this > > project. > > > No virus found in this incoming message. > Checked by AVG. > Version: 7.5.524 / Virus Database: 269.23.9/1419 - Release > Date: 5/7/2008 7:46 AM > > No virus found in this outgoing message. Checked by AVG. Version: 7.5.524 / Virus Database: 269.23.10/1421 - Release Date: 5/7/2008 5:23 PM
