Monday, December 28, 2009
Sunday, December 27, 2009
Waiting on A9 for Clearance
A9, almost at the end of road. Not many roads in SL run for 300+kms (it is 200kmX400km almost).
Tal Trees, Signature of Jaffna
Monday, December 21, 2009
Tuesday, December 15, 2009
Saturday, December 12, 2009
Thursday, December 10, 2009
Friday, December 4, 2009
Elinor Ostrom, the Arthur F. Bentley professor of political science and professor of public and environmental affairs at Indiana University has bagged the 8th Nobel prize for IU (For Economics). More details can be found in http://newsinfo.iu.edu/news/page/normal/12735.html. Congratulations!!.
Friday, November 27, 2009
Having said that, Correctness---fact that a system behaves according to its specification---is a property any system have to have, and systems that do have only other three are not very interesting. But it is worth noting that consistency and correctness are two different things, and an inconsistent system may be correct, given that its specification does not make any claims on consistency.
Tradeoff between scalability and consistency is well discussed under the topic of loose consistency. Amazon CTO, Werner Vogels has shed much light on the topic, and he argued that to create scalable systems, we have to let go of strong consistency guarantees like ACID (transactions). His post Eventually Consistent, revisted discusses this topic in detail. Those systems are Scalable, Correct, and Available, but only have loose consistency. Amazon's Dynomo is an example of such a system.
We can build Correct, Consistent, and Available systems using group communication, but those systems do not scale. Typically, the limit is considered to be 8-10 nodes in a group in group communication.
Finally, we can build a Scalable, Consistent, and Correct system by stopping all new requests whenever a change happen in a node untilthat change is disseminated in to all other nodes in the distributed system---even if there are thousands of nodes. Unfortunately, if updates are frequent, the system will reject messages most of the time, hence has poor availability.
Incorrect systems are bad, but neither of last three are bad by itself, and each of those are useful on some usecases. Hence they are useful tools in architect's tool box.
Actually, an interesting point is that those guys were never placed there by humans, rather one day, they decided to invade boat decks in Piper 39, and stayed there ever since (See http://www.cbsnews.com/stories/2009/11/24/eveningnews/main5764873.shtml). Crowd loved them, and soon they were a major attraction, which allows those snaky invaders to stay there unmolested
Tuesday, November 24, 2009
Friday, October 9, 2009
Basically Axis2 depends on commons http client security and it uses JSSE security. So setting following properties will do. However, httpclient also provides more deeper control.
Monday, September 21, 2009
Wednesday, September 16, 2009
Tuesday, September 1, 2009
Sunday, August 9, 2009
at Google". If you have noticed that I am thinking lot about user experience, the reason is that I am beginning to believe both in academia or or industry, impact on the end user is central to both understanding a problem and designing solutions.
Monday, August 3, 2009
Sunday, August 2, 2009
ICWS Talk 2: Application of Management Frameworks to Manage Workflow-Based Systems: A Case Study on a Large Scale E-science Project
Citation: Srinath Perera, Suresh Marru, Thilina Gunarathne, Dennis Gannon, Beth Plale, "Application of Management Frameworks to Manage Workflow-Based Systems: A Case Study on a Large Scale E-science Project," icws, pp.519-526, 2009 IEEE International Conference on Web Services, 2009
Abstract: Management architectures are well discussed in the literature, but their application in real life settings has not been as well covered. Automatic management of a system involves many more complexities than closing the control-loop by reacting to sensor data and executing corrective actions. In this paper, we discuss those complexities and propose solutions to those problems on top of Hasthi management framework, where Hasthi is a robust, scalable, and distributed management framework that enables users to manage a system by enforcing management logic authored by users themselves. Furthermore, we present in detail a real life case study, which uses Hasthi to manage a large, SOA based, E-Science Cyberinfrastructure.
Citation: Srinath Perera, Dennis Gannon, "Enforcing User-Defined Management Logic in Large Scale Systems," services, pp.243-250, 2009 Congress on Services - I, 2009
Abstract: The ubiquity of information technology, technological advances, and utility computing trends have motivated largescale systems, but managing and sustaining these systems is far from trivial. Automatic or semi-automatic monitoring and control are a potential solution to this problem. However, since management scenarios differ from system to system, a generic management framework that can manage a wide variety of systems should support user-defined management logic. This paper proposes a novel architecture that can manage large-scale systems according to user specified management logic that depends on both global and local assertions of the managed system. Furthermore, the paper demonstrates that despite having a global view of the managed system, a management framework can scale to manage most real world usecases.
Title: Enforcing User-Defined Management Logic in Large Scale Systems
Primary Advisor: Prof. Dennis B. Gannon
Thesis Committee: Prof. Dennis B. Gannon (Chair), Prof. Geoffrey C. Fox, , Prof. Beth A. Plale, Prof. David B. Leake, Dr. Sanjiva Weerawarana
Thesis can be found through ProQuest here (I paid and enabled open access, and therefore, you do not need an account to download it). Also there are two papers.
- Srinath Perera, Dennis Gannon, "Enforcing User-Defined Management Logic in Large Scale Systems," services, pp.243-250, 2009 Congress on Services - I, 2009
- Srinath Perera, Suresh Marru, Thilina Gunarathne, Dennis Gannon, Beth Plale, "Application of Management Frameworks to Manage Workflow-Based Systems: A Case Study on a Large Scale E-science Project," icws, pp.519-526, 2009 IEEE International Conference on Web Services, 2009
Due to advances in distributed systems, social motivations, and economic motivations, scales of systems are on the rise. In large-scale systems, changes--caused by failures, maintenance, and additions--are a norm rather than an exception, and therefore, manually keeping these systems running is difficult, if not impossible. System management, which monitors and controls systems, is a prominent solution to this problem.
However, management usecases differ from system to system, yet developing a specific management framework for each system defeats the purpose of building system management frameworks in the first place. Management frameworks that enforce management logic authored by users provide a solution for this problem. These frameworks enable users to change framework's decision logic to cater for user's specific requirements, and after deployed, they monitor and control target systems in accordance to the user-defined management logic. If these logic assert only a single component of the system, we call them local logic, and if these logic assert multiple components in the system, we call them global logic. The global logic depend on a global view about a system, which is non-trivial to support in large-scale systems. However, they enable users to reason about the target system explicitly and, therefore, provide a natural way to express management usecases.
This dissertation presents a new, dynamic, and robust management architecture that manages large-scale systems by enforcing user-defined management logic that depend on a global view of the managed system. Using empirical analysis, we have shown that it scales to manage 100,000 resources, which demonstrates that the architecture can manage most practical systems. This is a testament that despite its dependency on a global view of the managed system, a system management framework can manage systems in accordance to user-defined management logic and can still scale to manage most real world systems. Furthermore, we have demonstrated that the architecture is robust in the face of failures and stable with respect to different operational conditions.
Monday, July 27, 2009
Monday, July 20, 2009
Sunday, June 28, 2009
Friday, June 26, 2009
Saturday, June 20, 2009
One of the example of this trust the history can offer is Phalanx formation practised by Greeks (and later by Swiss) to great effect. One of the key features of the formation is that each man is protected not by his own shield, but by the one hold by the guys in the right, which gave each guy maximum freedom on the battlefield. Then, each man has literally placed his life in the hand of the guy to his right, and trust him to carry out the job. Result was a formidable formation---for instance, Aleksandr the Great used this to its full effect---which was legendry until after decades later Roman's out maneuver them in Battle of Magnesia through the flank (topic of interest, but not relevant to our discussion).
However, it is so easy to preach, and very hard to carry it out, because the trust is mutual. In game theory, Prisoner's dilemma shows how hard (probabilistically) for two untrusting guys to trust each other. For example, with the traffic in the Kandy road, it takes close to 2 hours to drive from Flower road to Gampaha---28km---which says we drive about 14km/hour. I am sure if we all can drive with order, we can get to the destination much faster---I mean how can you drive slower than 15km/h? However, none of us (including me who soon learnt the hard way that no quarter is given there) trust others to not to exploit it if we drive nicely.
So my concluding remark is that trust is such a great thing. Each of us by ourselves can only do so much, and it takes teams to make difference. The trust---or should I say faith, which assures each guy to play his own role, is the key in a great team. But, trust is mutual where it is so hard to keep and easy to break. Every time someone exploit someone else, he contributes to this inertia of untrust by making victim's heart bit more untrustful, and the society (or the team) as a whole takes a step back. You do it over a long time, we get where we are.
Thursday, June 18, 2009
Wednesday, June 17, 2009
Tuesday, June 9, 2009
Saturday, June 6, 2009
Sunday, May 24, 2009
Tuesday, May 19, 2009
After years, I felt that on this occasion Sri Lankans have united under same idea and hope we can figure out a way to make use of this opportunity, may be the best we have had after 1815. We must remember nobody will solve our problems for us. Not UN, not the west! Otherwise, why after all those years, we have never heard of a 3rd world nation that stood up with help of their aid and direction and become a developed nation? Why we only hear exploitations and Wars created by others? No! We are alone on this fight, nor will others fight it for us, nor can others understand the situation enough to fight it for us. It is up to us to figure out a way, and stand on our feet.
Wednesday, April 1, 2009
Everything about this cool app is great except for that today is the April 1st.
Sunday, March 29, 2009
I was at a talk by Genevieve Bell (Anthropologist), and one example I remembered is that how India supported connectivity to few rural villages (for E-Seva initiative I believe).
The village did not have connectivity, but had a bus that everyday go back and forth between the nearest town. What they did was install a Wifi receiver in the bus. When at the village, the bust automatically reads messages from a computer (again Wifi enabled) that is located at the bus stand, and when at the town, it sends all the messages to Internet, and brings back whatever messages the world has sent back.
India is going to have (may be already have) satellites, which cover its breadth, and then this solution will be obsolete. Nevertheless, it strikes me by its simplicity (rather it is outof the box). Different versions of the same idea can be find in other places. For example, in Ploar Grid the use case is like follows (From what I heard). There are lot of equipments installed that continuously collect data across a large region, and rather than setting up a communication network, a small plane flys through the area and collect data from equipments via Wifi. Similarly professor Tanambaum said "never underestimate the bandwidth of truck full of tapes", and in the paper "Above the Clouds: A Berkeley View of Cloud Computing" authors recommended that it could be cheaper to Fedex the disks to the cloud computing provider.
Also, there are another set of use cases are emerging. With use cases like Large Hadron Collider and Large Telescopes, the size of data is going out of bounds. For example, March IEEE Spectrum reported an optical receiver with 640Gb/sec. With these systems, peta bytes (10^15) of data are common. Problem is even with 10Gb/sec Ethernet (yep Teragrid is connected via 10Gb/sec Ethernet) takes 20 minutes to send 1 tera bytes, and it takes 11 days to transfer a full peta byte. Therefore, it might be common in the future that we receive literally a container full of data.
These kinds of asynchronous (with very big latencies) communications provide different kinds of interactions, and call for different types of use cases. It is a challenge to figure out how best to use them, and how best to present them to the user. For example, client side validation and preprocessing is very important, and it might make sense to add additional data, which might be useful to the result. For example, if you are searching Google through this way (nobody will if they have a choice), you might need to return all the results not only links (may be small crawl of first few results) etc.
Saturday, March 28, 2009
In one or two places it does over simplify (e.g. with computers, just one small piece added part). However, there are truths in it. Actually, more or less "watch TV -> You sucks -> go and work -> buy things -> watch TV" is part of our lives. It is more less the effect imposed by criticizing eyes driven by styles and trends. I do not know how true are the numbers, but if 50% (they say it 99%) of things are thrown off in 6 months, we have a problem.
The original can be found in The Story of Stuff with Annie Leonard.
Friday, March 27, 2009
Also the blog post  by James Governor, argues that hardware as the service model of Amazon is the way to go. I agree that nice simple model of AWS simpler, because it enables users to port with relatively less changes, and of course "simpler is better". However, the higher level of abstractions like App Engine could provide more features like failover, or auto scaling (I mean auto scaling the application, not just increasing machines). Among questions are how general will those features, how much changes do they need to exiting systems, can they solve associated hard problems?
 Neal Leavitt, "Is Cloud Computing Really Ready for Prime Time?," Computer, vol. 42, no. 1, pp. 15-20, January, 2009.
 Amazon Web Services: an instance of weakness as strength
Thursday, March 26, 2009
My topic is "Enforcing User-Defined Management Logic in Large Scale Systems". My adviser is prof. Dennis Gannon, and the rest of the committee are prof. Beth Plale , prof. Geoffrey Fox, prof. David B. Leake and Dr. Sanjiva Weerawarne. I would like to thank prof. Gannon and the rest of the committee whose insights and encouragements made this thesis possible.
Furthermore, I would like to heartily thank Dr. Sanjiva, first of all for convincing me to read for a Ph.D---as my friends know, I was pretty decided not to do one by my third year at Moratuwa--- and for his unceasing attention, help, and advice though years. If not for him, none of this would have possible. Also my heartfelt thinks go to my wife, Miyuru, my parents, and my bother, for their help and support.
All Six people who originally worked on Axis2 from LSF are in grad school (Jaliya, Ajith, Chathura, Eran, Deepal), and also there are many more who followed them (more detail here). We will see many Ph.Ds from these people soon. However, earning Ph.Ds will be only a small step towards where we want to go; there is lot of hard work ahead.
Friday, March 20, 2009
Tuesday, March 17, 2009
Friday, March 6, 2009
Sunday, March 1, 2009
Wednesday, February 18, 2009
One thing international community does not realize (or rather ignore) is that they are susceptible to manipulation. There are many ways to fight a war, and if one do want to do something bad, either he can do it himself or manipulate information to get someone else to his dirty work (someone powerful enough!). Since international community does not bother to check the background, check history, and do a independent evaluation, rather pass judgment by case by case, they are susceptible to manipulation. That is how they gain mistrust.
Friday, February 13, 2009
Saturday, February 7, 2009
and Libertarian Answers" By David Bergland very interesting. It is presented as a Q&A session, and one thing I take home from that is there is no one correct answer.
Thursday, February 5, 2009
Wednesday, January 21, 2009
Tuesday, January 20, 2009
Also this is the Lincoln's second inaugural address, which is considered one of the best, and it includes the famous quote, "With malice toward none; with charity for all; with firmness in the right ....--Abraham Lincoln", and John F. Kennedy: Inaugural Address.
Monday, January 19, 2009
Sunday, January 18, 2009
Thursday, January 15, 2009
But, his evidence does not run very deep, mostly they are personal observations, however, when I think about my own net browsing habits and what I seen others do, I feel may be there is a ring of truth in it. (However, at Grad school, there is no shortage of serious reading!! I am safe :)). Nevertheless, as he himself pointed out, when "writing was invented", and "printing was invented" people complained lot, so on and so forth, and at each case our brained proved to up to the task. Humans are good at adapting, and with luck our brain will continue to do so.