Mustafa Atik - Personal Blog

In computer systems, caches are used to diminish the slowness of main memory which is larger and cheaper than cache memory. Caches are faster because not far from CPU and not as large as main memory. In modern computers, there may be more than one cache memory. The layers composed a memory hierarchy. The memory hierarchy is sometimes called an illusion to processors because a processor can have as large and fast a memory as it needs at the level of reasonable cost. In short, from a broader perspective it is easy to understand why memory hierarchies are needed; however, to understand how it works you need to narrow the perspective, e.g. taking account only two memory layers at one time. Key concepts are: cache miss and hit ratios. memory and cache and average access speed memory size, cache size block or cache line size set size direct mapping, fully associative mapping, set associative mapping address partitioning (tag bits, index/set bits, block bits) replacement algor

In the class of SWE 514 Computer Systems , I am studying low-level concepts about cpu and memory design. Although I am totally abstracted from them in daily programming life, I think If you are a software developer it is good to catch at least a glimpse of how memory management works, regardless you write low-level or high-level programs. In many respect, management burdens are being carried out by operation systems; however, sometimes having knowledge about these may help you in terms of performance or security issues. I am not going to explain what the memory management is here; instead, I will share some useful resources. The article titled " Principles of virtual memory " by Carl Burch and Hendrix College seems to me that it covers most of sides of virtual memory concept very concisely. After reading it, you will understand why virtual memory exists and which parts of it are actually crucial. In the following youtube playlist, virtual memory concept is discussed as why w

In this article, I will show you how to inject Android views using Roboguice and Butterknife, and how to use dependency injection using Roboguice. You can infer that Butterknife is not a dependency injection library. Why do we need them? If you start to develop programs beyond “hello world” with java or all other languages, you probably want to get rid of some repetitive, cumbersome boilerplate coding parts. Indeed, we should focus on logic, not on metaprogramming. For example, in Android development, you get view references as follows: In this code, we only want to change a textView’s text and show the labels of the two buttons. What we want is called our program’s logic. As it is obvious we have to write a lot of statements to achieve such a simple task. Now try to guess what happens if you have a lot of views, more than just two… Butterknife helps us to focus on logic With this library, it is easier for us to create view references. So you can write a shorter version

We have recently had a "to many open files" problem in one of our Mongodb servers. Mongodb kept saying "Out of file descriptors. Waiting one second before trying to accept more connections." and accept no more connections. The first thing came to our mind was that the reason is too much load, our mongodb servers were no longer enough to carry it. But it was wrong. After first research it became clear that it was because of linux's user limits, so our wrong decision: running mongodb servers with the root user. In linux systems, every user has some limits which decide how much system resources they are allowed to consume. These limits prevent one devil user to drain all the system and to make other users to starve of resources. In our linux servers, root user had lower limits than mongodb's suggested limits. Even if the root user had the suggested limits, we could have had the problem any way. Because root user is responsible for other operational works, not

Bir kümedeki elementlerin benzerliğini ölçen, benzerlik puanı üreten avantajı ve dezavantajı duruma göre değişen algoritmalar bulunmaktadır. Collaborative Intelligence kitabında Euclidean Distance hesaplaması ile film eleştirmenleri arasındaki benzerlik hesaplanmıştır. Senaryoda, kişiler çeşitli filmlere puan vermişlerdir ve bu puanlar üzerinden bir kişinin diğer insanlarla arasındaki benzerlik hesaplanmıştır.Birkaç ekleme dışında kodların tamamını kitaptaki gibi aktarıyorum. from math import sqrt def sim_euclidan_distance(prefs, person1, person2): si={} for item in prefs[person1]: if item in prefs[person2]: si[item]=1 if len(si)==0: return 0 sum_of_squares=sum([ pow( prefs[person1][item]-prefs[person2][item], 2) for item in prefs[person1] if item in prefs[person2] ]) return 1/(1+sqrt(sum_of_squares)) critics={ 'Mustafa': { "The Matrix": 5, "The Godfather": 5, "Se7en": 3, "Babel": 2, "Troy": 4, &

Code is known to be written something by programmers for computers to do some tasks. Currently commanding by a language which is near to computers is not necessary for most use-cases. When we create a file on a disk, in most use cases we do not care how this process is carried out. When we fetch an URL’s content, we enjoy concise statements like ‘fetch_content(url)’, get_url_content(url)’. We are not interested in how, but what. We are migrating from the imperative paradigm to the declarative one. So that we invented high level languages such as Python, C#, Java, PHP; which are more similar to a natural language.

Facebook’s data science team published a post in which they claim it is possible to predict a football team’s performance mining emotions of its fans. The post tells us before a kick-off, fans seem positive. But the volume of positive emotion is higher in the fans who support the better team. After the match, the winner’s fans feel very high positive emotion, on the other hand other team’s fans feel negative. Actually we do not need any study to predict this correlation between teams and their fans. It is obvious when a team wins, its fans get happy and so they post positive status messages. Yet I think this study is not trivial. Every study does not necessarily bring about a breakthrough.

At last, I’ve made a strong decision to migrate from PHP to Python. Leaving a tool, leaving your bread basket would not be an easy decision if you used it almost for eight years. Otherwise, I believe that sometimes with a little bit courage to leave your conform zone and a lot of curiosity you can get a better bread basket, maybe a jar of jam too. if you want to be a sea, you must give up being a drop. Why am I leaving PHP? Actually I am not leaving PHP totally, but switching my primary language to Python because my works have been changing. Most of work required from me is related to natural language processing(NLP), machine learning(ML) techniques. And I, and many other developers, find Python much more capable to deal with this kind of works. It has already many libraries, tools, frameworks for NLP and ML. Another reason is that I think web programming will not grow as much as an intelligent system. Maybe I am wrong, but there is no doubt the future is about intelligent systems.

In my programming circle, I’ve encountered many programmers who give most of their attention to debugging software bugs. And this is not bad, but not enough to be efficient. Efficiency includes both preventing possible bugs and removing existent one. Let me explain what programming and debugging are with a doctor-patient analogy, which I’ve just made out. As we all know, to be healthy the first thing we must do is not eating too much and junk food, doing enough exercise, not smoking, and not drinking too much drink. The list may vary for each individual. Even though we do all these, it is always possible to be ill. In view of possibility of being ill, we always require doctor to be around in case of anything. For example, not to be a diabetic you need control your eating. But does the controlling make medical improvement against diabetes unnecessary? Not at all. We need enough efficient cure to diabetes, so medical and science works on this. We need doctors. Analogously, in software