Cheetah vs. Enzo Ferrari



3.65 seconds (0-100km)3.5 seconds, (0-100km)
in off-road conditions.
variable intake manifold2 variable nostrils
rear wheel drivefour-leg drive

NoHadoop? NoMapReduce?


After seen this post, I bought the domains nohadoop.org and nomapreduce.org to build a community and share knowledges about these topics.

MapReduce provides easy-to-program but, you can realize that it's only under specific conditions. In short, the many practical problems requires more flexible and versatile computing system. Actually, we (Apache Hama team) was also really skeptical about use of the MapReduce in the area of linear algebra, machine learning, graph algorithms ,.., etc, and we got rid of dependencies of MapReduce and HBase in the end.


The development of technology is always inevitable, irreversible and unavoidable!

Ancient Aliens? It's only a plausible fantasy.

I watched 'Ancient Aliens' today. There are some ideas and feelings that sound plausible but given just a wee bit of thought can be shown to border on the fantasy.

First there is a west-centered thinking. For e.g., bible, westen technologies, ... , etc. Do you know that there are many more than 100 pyramids in Manchu? Moreover, some of them is bigger and 2 thousand years older than egyptian great pyramid. Why we didn't know about them? Only korean knows. Because of the chineses stopped and restricted excavation works, since they are finding korean artifacts from there.

Anyways .. I was trying to say that, we don't know our history enough to talk about. I think, it is only a kind of plausible fantasy from our lack of knowledge, like humans created god in man's image. What do you think?

Quorum algorithm of the Zookeeper

The Apache Zookeeper is a coordination service for distributed applications, like a Google's Chubby. Many projects uses zookeeper, and we (Apache Hama) also uses zookeeper for barrier synchronization of Bulk Synchronous Parallel computing framework.

Today, I surveyed more about paxos and dynamic quorum of Zookeeper project, to renaming the class name of org.apache.hama.zookeeper.QuorumPeer. Because of documentation is not enough, I didn't know what is the meaning of quorum and the term of "quorum" was somewhat odd to me.
But, the "org.apache.hama.zookeeper.QuorumPeer" is proper name!! xD

So, what is the Quorum and why do we need a Quorum?

According to Wikipedia, Quorum is the minimum number of members of a deliberative body necessary to conduct the business of that group. Ordinarily, this is a majority of the people expected to be there, although many bodies may have a lower or higher quorum.

As you know, a Fault-Tolerant mechanism is one of the important functions of distributed system. Quorum algorithm is used to prevent the split-brain condition. When split-brain condition occurrs, according to the Quorum algorithm, zookeeper determines the "Primary Patrition" and "Secondary Partition". Then, the servers in primary group are receives and processes user's request, and the servers in secondary group are becomes read-only mode. When recovered from split-brain condition? They will be merged to one partition again. Interanally, zookeeper uses atomic broadcast protocol instead of Paxos.

무한의 세계

무한 집합의 크기 Cardinality , 즉 원소의 개수를 수학에서는 '농도'라고 말한다. 유한 집합의 크기는 그대로 원소의 개수 이지만, 무한 집합의 경우는 원소의 개수를 낱낱이 셈하는 것은 불가능하기 때문에 '농도'라...