## Posts

### Black Friday theory

Black Friday is a selling race over the gift budget that has the peak around the start of December What is the lowest possible price on "Black Friday"? Sellers will try to make this unpredictable. However, there are certain price strategies that any rational seller should apply. This can give you hints about the likelihood of obtaining a lower price on Black Friday, Cyber Monday and similar. Why having price cuts at all? Normally, any producer or seller would want to have the highest gain from the products he sales, therefore higher price is desirable. However, selling more many pieces of a product might bring higher gain than the loss from the price cut. Also, a product that is not sold brings no revenue, while selling slightly over the acquiring price still brings some money. What are the reasons for doing price cuts? "Black Friday" is not only a period of gratefulness, it is also a day close to the winter holidays, when many people buy gifts for others

### We only have models, not knowledge

We know that water boils at 100 degrees Celsius, right? Or not ; on mount Everest the water boils at around 70 degrees Celsius, so you can't even boil an egg . Ok, we have a more complex model that links the boiling temperature with pressure, but even that model is not exact at any given pressure. On some temperatures, our linear models fail, for example water cooled below 4 degrees Celsius will not continue to get denser, but it will actually expand, allowing the cold water to float on the surface until it becomes ice. In general, lower temperature would predict lower density in substances. There is nothing in the common physical laws that would predict such anomaly  in water, while we can later construct even more complicated models to explain what is happening with water.

### Unequal inflation

It's common knowledge that if you print more money, you will produce inflation. However, things are more complex than that. You can have both inflation and deflation in the same time. More often, we have relatively low inflation on common products and high inflation on specific products - think real estate. Money velocity First, there is that "money velocity" that equals the equation Products * Price = Money * Velocity . The money velocity is intuitive, but cannot be practically measured except from this equation - thanks to my namesake friend for this idea.

### Data Consistency and the "Theory of relativity"

"If a tree falls in a forest and no one is around to hear it, does it make a sound?" If a system has an inconsistency but nobody can observe it, is it still an inconsistency? Introduction We need to scale data processing systems geographically to achieve lower Latency and (at least partial) Availability in case of network Partitioning. But CAP / PACELC tells us that we cannot achieve strong Consistency in this case. When we increase the Consistency requirements, we have to accept lower Availability and higher Latency. What is the minimum consistency level that we need? If eventual consistency is enough for your system, things are pretty clear and relatively simple. Most probably you want to achieve Strong Eventual Consistency that is relatively cheap and provides nice guaranties. For this you will have to you something like CRDT . Some theoretical results assure us that you cannot find something way cleverer than CRDT that achieves Strong Eventual Consistency. Often, you ha

### Religions are (Software) Operating Systems

It is hard to live without a religion. Each religion comes with its set of APIs, for blessing and cursing, for forking a process child and for being sure a dying process doesn't become a zombie. Religions come with their set of protection mechanisms and their corresponding violation errors and punishments.

### Flow consistency - read-your-writes consistency

Consistency, Availability and low Latency in Distributed systems - part 2 (workarounding the CAP/PACELC theorems)   See also: " Cache and Data Consistency in Distributed systems (CAP/PACELC/CRDT) - part 1 "   TL;DR Full strong Consistency in geographically Distributed systems can only be achieved by sacrificing Availability (per CAP theorem) and with prohibitive Latency costs (per PACELC theorem). However, we can still design consistent enough systems that continue to function when one geographical region is down and without paying the inter-region latency most of the time. While eventual Consistency is OK many times, there are still cases when we want a strong read-after-write consistency for certain read-after-write flows. There is an optimum design that assures strong Consistency inside read-after-writes flows . Arguably, this is the highest Consistency level that can be assured without a prohibitive impact on Availability and Latency.

### Devil's offer

Imagine that humanity is offered the following deal: All living humans will enjoy 100 more years of healthy and happy life, finished by a peaceful death in sleep. Immediately after signing the deal, humans will forget the deal and will not worry about this "deadline". If you sign the deal, no human will even experience any suffering. As life will be extended to 100 years from now regardless of the starting age, no human will even witness the death of another human. Even old people would enjoy a healthy and happy life, becoming physically young again and regaining their mental capacity - without losing their experience. Each life will be full of accomplishments, not only by material welfare, but also with most spiritual accomplishments that a human can reasonably expect. Children will still be born, parents will still be happy about them - even more so, because all would go smooth with no worries and no accidents. People would live happily and without any worry until the &quo

### Morality and killing

Killing is morally wrong universally, for most people adhering to a moral system, right?  What about killing an aggressor that tries to kills hundreds of people in your community? Suddenly that killing to save the life of many innocents does not seem so repellent for most people, don't you agree? What if the killing of an aggressor is the only solution to save the life of a member of your family? Even many religious people would consider such defensive killing the right thing to do if there is no other solution.