Hi, I presume you have read the percolator paper. The design there uses a single ts oracle, and BigTable itself as the transaction manager. In omid, they also have a TS oracle, but I do not know how scalable it is. But using ZK as the TS oracle would not work, since ZK can scale up to 40-50K requests per second, but depending on the cluster size, you should be getting much more than that. Especially considering all clients doing reads and writes has to obtain a TS. Instead what you want is a TS that can scale to millions of requests per sec. This can be achieved by the technique in the percolator paper, by pre allocating a range by persisting to disk, and an extremely lightweight rpc. I do not know whether Omid provides this. There is a twitter project https://github.com/twitter/snowflake that you might want to look at.
Hope this helps. Enis On Sun, Apr 21, 2013 at 9:36 AM, Michel Segel <michael_se...@hotmail.com>wrote: > Time is relative. > What does the timestamp mean? > > Sounds like a simple question, but its not. Is it the time your > application says they wrote to HBase? Is it the time HBase first gets the > row? Or is it the time that the row was written to the memstore? > > Each RS has its own clock in addition to your app server. > > > Sent from a remote device. Please excuse any typos... > > Mike Segel > > On Apr 16, 2013, at 7:14 AM, yun peng <pengyunm...@gmail.com> wrote: > > > Hi, All, > > I'd like to add a global timestamp oracle on Zookeep to assign globally > > unique timestamp for each Put/Get issued from HBase cluster. The reason I > > put it on Zookeeper is that each Put/Get needs to go through it and > unique > > timestamp needs some global centralised facility to do it. But I am > asking > > how practical is this scheme, like anyone used in practice? > > > > Also, how difficulty is it to extend Zookeeper, or to inject code to the > > code path of HBase inside Zookeeper. I know HBase has Coprocessor on > region > > server to let programmer to extend without recompiling HBase itself. Does > > Zk allow such extensibility? Thanks. > > > > Regards > > Yun >
