Are these the good links for the Yahoo Benchmarks? http://www.brianfrankcooper.net/pubs/ycsb-v4.pdf http://research.*yahoo*.com/files/ycsb.pdf
Kevin On Sat, May 8, 2010 at 3:00 PM, Ryan Rawson <ryano...@gmail.com> wrote: > hey, > > HBase currently uses region count to load balance. Regions are > assigned in a semi-randomish order to other regionservers. > > The paper is somewhat correct in that we are not moving data around > aggressively, because then people would write in complaining we move > data around too much :-) > > So a few notes, HBase is not a key-value store, its a tabluar data > store, which maintains key order, and allows the easy construction of > left-match key indexes. > > One other thing... if you are using a DHT (eg: cassandra), when a node > fails the load moves to the other servers in the ring-segment. For > example if you have N=3 and you lose a node in a segment, the load of > a server would move to 2 other servers. Your monitoring system should > probably be tied into the DHT topology since if a second node fails in > the same ring you probably want to take action. Ironically nodes in > cassandra are special (unlike the publicly stated info) and they > "belong" to a particular ring segment and cannot be used to store > other data. There are tools to do node swap in, but you want your > cluster management to be as automated as possible. > > Compared to a bigtable architecture, the load of a failed regionserver > is evenly spread across the entire rest of the cluster. No node has a > special role in HDFS and HBase, any data can be hosted and served from > any node. As nodes fail, as long as you have enough nodes to serve > the load you are in good shape. The HDFS missing block report lets you > know when you have lost too many nodes. Nodes have no special role and > can host and hold any data. > > In the future we want to add a load balancing based on > requests/second. We have all the requisite data and architecture, but > other things are up more important right now. Pure region count load > balancing tends to work fairly well in practice. > > 2010/5/8 MauMau <maumau...@gmail.com>: > > Hello, > > > > I got the following error when I sent the mail. > > > > Technical details of permanent failure: > > Google tried to deliver your message, but it was rejected by the > recipient > > domain. We recommend contacting the other email provider for further > > information about the cause of this error. The error that the other > server > > returned was: 552 552 spam score (5.2) exceeded threshold (state 18). > > > > The original mail might have been too long, so let me split it and send > > again. > > > > > > I'm comparing HBase and Cassandra, which I think are the most promising > > distributed key-value stores, to determine which one to choose for the > > future OLTP and data analysis. > > I found the following benchmark report by Yahoo! Research which evalutes > > HBase, Cassandra, PNUTS, and sharded MySQL. > > > > http://wiki.apache.org/hadoop/Hbase/DesignOverview > > > > The above report refers to HBase 0.20.3. > > Reading this and HBase's documentation, two questions about load > balancing > > and replication have risen. Could anyone give me any information to help > > solve these questions? > > > > [Q1] Load balancing > > Does HBase move regions to a newly added region server (logically, not > > physically on storage) immediately? If not immediately, what timing? > > On what criteria does the master unassign and assign regions among region > > servers? CPU load, read/write request rates, or just the number of > regions > > the region servers are handling? > > > > According the HBase design overview on the page below, the master > monitors > > the load of each region server and moves regions. > > > > http://wiki.apache.org/hadoop/Hbase/DesignOverview > > > > The related part is the following: > > > > ---------------------------------------- > > HMaster duties: > > Assigning/unassigning regions to/from HRegionServers (unassigning is for > > load balance) > > Monitor the health and load of each HRegionServer > > ... > > If HMaster detects overloaded or low loaded H!RegionServer, it will > unassign > > (close) some regions from most loaded H!RegionServer. Unassigned regions > > will be assigned to low loaded servers. > > ---------------------------------------- > > > > When I read the above, I thought that the master checks the load of > region > > servers periodically (once a few minutes or so) and performs load > balancing. > > And I thought that the master unassigns some regions from the existing > > loaded region servers to a newly added one immediately when the new > server > > joins the cluster and contacts the master. > > However, the benchmark report by Yahoo! Research describes as follows. > This > > says that HBase does not move regions until compaction, so I cannot get > the > > effect of adding new servers immediately even if I added the new server > to > > solve the overload problem. > > What's the fact? > > > > ---------------------------------------- > > 6.7 Elastic Speedup > > As the figure shows, the read latency spikes initially after > > the sixth server is added, before the latency stabilizes at a > > value slightly lower than the latency for five servers. This result > > indicates that HBase is able to shift read and write load > > to the new server, resulting in lower latency. HBase does > > not move existing data to the new server until compactions > > occur2. The result is less latency variance compared to Cassandra > > since there is no repartitioning process competing > > for the disk. However, the new server is underutilized, since > > existing data is served off the old servers. > > ... > > 2 It is possible to run the HDFS load balancer to force data > > to the new servers, but this greatly disrupts HBase’s ability > > to serve data partitions from the same servers on which they > > are stored. > > ---------------------------------------- > > > > MauMau > > > > > > >
