Developers Club geek daily blog

How to cover with monitoring all layers of infrastructure

1 year, 2 months ago
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Somehow I considered that 1 minute of idle time of hh.ru on weekdays affects about 30 000 users in the afternoon. We constantly solve a problem of decrease in number of incidents and their duration. We can reduce quantity of problems the correct infrastructure, architecture of the application is a separate subject, we will not take it in attention yet. Let's talk better about how quickly to understand what occurs in our infrastructure. Here just we are also helped by monitoring.

In this article on the example of hh.ru I will tell and I will show how to cover with monitoring all layers of infrastructure:
  • metrics client-side
  • metrics from frontends (nginx log)
  • network (that can be got from TCP)
  • application (log)
  • database metrics (postgresql in our case)
  • operating system (cpu usage can be useful too)

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Performance measurement of functions in JavaScript

1 year, 2 months ago


Performance always played a key role in the software. And in web applications its value is even higher as users can easily go to competitors if the website made by you works slowly. Any professional web developer has to remember it. Today it is still possible to apply successfully the mass of old acceptances of optimization of performance, like minimization of amount of requests, use of CDN and not use to rendering of the blocking code. But the more developers apply JavaScript, the problem of optimization of its code becomes more important.

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How to predict a stock price: Algorithm of adaptive filtering

1 year, 1 month ago


The group of the Brazilian scientists published the research devoted to creation of the tool for a prediction of behavior of the assets bargaining in stock market. In work the detailed description of a method and method of calculations for similar forecasts is submitted. We present to yours the most interesting moments of this document.

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Under Redis cowl: Hash table (part 2) and List

1 year, 2 months ago
In the first part I told that a hash the table is a few LIST, SET and SORTED SET. You judge — LIST consists of ziplist/linkedlist, SET consists of dict/intset, and SORTED SET is ziplist/skiplist. We already considered the dictionary (dict), and in the second part of article we will consider structure of ziplist — the second most often applicable structure under Redis cowl. Let's look at LIST — the second part of its "kitchen" is simple implementation of the chained list. It is useful to us attentively to consider often mentioned council about optimization a hash of tables through their replacement by lists. Let's consider how many it is required to memory on overhead costs when using these structures what price you pay for economy of memory. Let's sum up the results during the work about a hash as tables, when using the coding in ziplist.

Last time we finished that ziplist of 1,000,000 keys saved with use occupied 16 MB of random access memory whereas in dict the same data demanded 104 MB (ziplist 6 times less!). Let's understand what price:

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Animation of the falling snow is one Canvas more effective than animation on DOM several times

1 year, 1 month ago
. In comparison with native JS on the DOM elements, implementation of animation algorithms on Canvas is usually more productive many times over. It is the known fact (but with features for small number of particles as it will become clear later), and it can find implementation so everything disturbing traditional under NG, but driven by rational users of "the falling snow". That it was not enough loading, in recent years it is considered a good form "to start" snow on the website scarcely noticeable, with the minimum quantity of snowflakes (5-15). Here both the effect is, and honor loads of the processor any.

Therefore, so far to NG some more days still winter, I suggest to arrange a hakatonchik on implementation of the best algorithms on a kanvasa and their analogs on DOM, having taken as a basis generally ancient native algorithms which as at most turned back in jQuery plug-in that it was convenient to connect. The most part of these algorithms does not proportion load of the processor or is made inefficiently therefore even at small number of snowflakes load the processor for 100%. Here an example of a review article where more than 10 implementations are considered, not everything, meeting in the nature. In addition, we will consider several electees to receive a backlog on development of algorithm and implementation it with good efficiency (5-6 more options will turn out). On this basis it is possible to construct completion.

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In total for watchOS

1 year, 3 months ago


We paid attention to active work on applications for watchOS of the graduate of our Accelerator, decided not to lag behind and promote active use of a new platform.

The list of frameworks, libraries and examples of applications for watchOS is given below.

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Forward translation of MBLTdev

1 year, 3 months ago
Good news!
Everything at whom it is impossible to visit the Second international conference of the mobile MBLTdev developers on November 17 in Digital October, will be able to look at action on the air!

This year the program of conference includes reports for mobile developers and for heads of the IT companies, and also seminars for developers. The audience online of broadcasting will be able to visit the round table devoted to mobile ecosystems and to hear reports from the best mobile developers and interview with the most interesting speakers of conference.


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Open-source of implementation of domestic cryptostate standard specifications

1 year, 2 months ago
At the weekend decided to look for open-source of implementation of domestic cryptographic standards. First of all interested new: a hash function of Stribog (GOST P 34.11-2012), the Grasshopper (State standard specification P 34.12-2015) and the EDS (GOST P 34.10-2012 or 2001 (without 512 bits)). Old GOST 28147-89 specially did not look for as to find its implementation there are no problems for a long time.
So, let's look what turned out. At once I warn that did not check a correctness of implementations.

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Work on design of space reptiloid: wandering on labyrinths of opportunities

1 year, 1 month ago


The normal such reptiloidny race arising from abysses of deep space. Bang-bang from the laser weapon from all boards! Then rapprochement and a boarding, in completion of attack bloody slaughter onboard the seized vessel. Reptiloida – men of his word: told "all we will cut", means all will cut who would doubt. Also are dissolved in frosty blackness, only saw them.

However, investigation informed. If to open the game Encyclopedia, it will become clear:

Exact coordinates of basing of a civilization of Uchcha-Ta are unknown. It is considered to be that it is the planet Drro-Adda (so-called Planeta-Mat) of planetary system around the W-maiden (star accumulation TDD67, the "spread jellyfish" type, a spectral class is unknown).

So, the residence is set: after piracy attack on the peace ships of a reptiloida disappear on native Planetomateri.

And what it gives me as to the art director in sense of hints on design of the character? And anything.

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Travel startups. As programmers on the trillionth market are enticed: kofaunder, vacancies, hackathons

1 year, 3 months ago
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Yandex, Rambler, Qiwi outlined checkboxes the territory in the field of a travel services. Dvizhukh around the market of travel gains steam, and many do not hesitate and use expression of next big thing.

Soon conference on a travel startups where it will be possible to try the hand starts and to listen to the concentrated analytics from experts and practicians, to understand that occurs in the market of internal tourism. More and more people will have a rest in Russia soon, but whether the market is ready to it? What happens to a travel startups and as key players of the market react to it?

As DZ — this article that in 10-20 minutes to understand that it is demanded in the world and what IT specialists in great demand.

Here only some ideas for a travel startups which I found in the course of preparation of article: Uber for sailing vessels, Airbnb for boats, guides volunteers, mobile guides and assistants, tickets and settling in the last hour on discounts, sharing of the routes, a netvorking for entrepreneurs during travel, a virtual incubator of a travel startups, an earning of points for the settlement of guests, a karsherring for travelers, unique User eXperience during travel, gastronomic features, purchase of goods of duty-free even before passing of passport control, augmented reality (owners of smartphones can see historical sights such what they were initially), zhelezyachny startups (fastening of GoPro to the smartphone), krosskhostelsky services and so forth.

Under a cat a travel startups selection (including useful and for an udalyonka) on which it is possible to look and draw for himself conclusions, the list of vacancies to understand what programmers the industry, and also descriptions of several (last) hackathons needs.

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