The Yahoo! research link is the most recent one afaik... Thats the one submitted to SOCC'10
On Sat, May 8, 2010 at 3:36 AM, Kevin Apte <technicalarchitect2...@gmail.com > wrote: > 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 > > > > > > > > > > > >
