High performance

12.3 million of concurrent WebSockets

• High performance,
• C++,
• *nix,
• Lua

• Recovery Mode

How to speed up LZ4 decompression in ClickHouse?

• Яндекс corporate blog,
• High performance,
• Open source,
• C++,
• Big Data

When you run queries in ClickHouse, you might notice that the profiler often shows the LZ_decompress_fast function near the top. What is going on? This question had us wondering how to choose the best compression algorithm.

ClickHouse stores data in compressed form. When running queries, ClickHouse tries to do as little as possible, in order to conserve CPU resources. In many cases, all the potentially time-consuming computations are already well optimized, plus the user wrote a well thought-out query. Then all that's left to do is to perform decompression.



So why does LZ4 decompression becomes a bottleneck? LZ4 seems like an extremely light algorithm: the data decompression rate is usually from 1 to 3 GB/s per processor core, depending on the data. This is much faster than the typical disk subsystem. Moreover, we use all available CPU cores, and decompression scales linearly across all physical cores.

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From High Ceph Latency to Kernel Patch with eBPF/BCC

• Selectel corporate blog,
• High performance,
• Configuring Linux,
• Server Administration

There are a lot of tools for debugging kernel and userspace programs in Linux. Most of them have performance impact and cannot easily be run in production environments. A few years ago, eBPF was developed, which provides the ability to trace the kernel and userspace with low overhead, without needing to recompile programs or load kernel modules.

There are now plenty of tools that use eBPF and in this article, we’ll explain how to write your own profiling tool using the PythonBCC library. This article is based on a real issue from the production environment. We’ll walk you through solving the problem and show how existing bcc tools could be used in some cases.

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danikin May 13, 2019 at 12:02 PM

Citymobil — a manual for improving availability amid business growth for startups. Part 5

• Mail.ru Group corporate blog,
• High performance,
• System Analysis and Design,
• Start-up development,
• Product Management

This is the final part of the series describing how we’re increasing our service availability in Citymobil (you can read the previous part here). Now I’m going to talk about one more type of outages and the conclusions we made about them, how we modified the development process, what automation we introduced.

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danikin May 7, 2019 at 12:43 PM

Citymobil — a manual for improving availability amid business growth for startups. Part 4

• Mail.ru Group corporate blog,
• High performance,
• System Analysis and Design,
• Start-up development,
• Product Management

This is the next article of the series describing how we’re increasing our service availability in Citymobil (you can read the previous parts here: part 1, part 2, part 3). In further parts, I’ll talk about the accidents and outages in detail.

1. Bad release: database overload

Let me begin with a specific example of this type of outage. We deployed an optimization: added USE INDEX in an SQL query; during testing as well as in production, it sped up short queries, but the long ones — slowed down. The long queries slowdown was only noticed in production. As a result, a lot of long parallel queries caused the database to be down for an hour. We thoroughly studied the way USE INDEX worked; we described it in the Do’s and Dont’s file and warned the engineers against the incorrect usage. We also analyzed the query and realized that it retrieves mostly historical data and, therefore, can be run on a separate replica for historical requests. Even if this replica goes down due to an overload, the business will keep running.

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danikin April 29, 2019 at 11:51 AM

Citymobil — a manual for improving availability amid business growth for startups. Part 3

• Mail.ru Group corporate blog,
• High performance,
• System Analysis and Design,
• Start-up development,
• Product Management

This is the next article of the series describing how we’re increasing our service availability in Citymobil (you can read the previous parts here and here). In further parts, I’ll talk about the accidents and outages in detail. But first let me highlight something I should’ve talked about in the first article but didn’t. I found out about it from my readers’ feedback. This article gives me a chance to fix this annoying shortcoming.

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morozovsk April 29, 2019 at 01:15 AM

Statistics and monitoring of PHP scripts in real time. ClickHouse and Grafana go to Pinba for help

• High performance,
• PHP

• Tutorial

In this article I will explain how to use pinba with clickhouse and grafana instead of pinba_engine and pinboard.

On the php project pinba is probably the only reliable way to understand what is happening with performance. But usually people start to use pinba only when problems are already observed and it isn't clear where to look in.

Often developers have no idea how many RPS each script has. So they begin to optimize starting from places that seem to have problem.

Someone is analyzing the nginx logs, and someone is slow queries in the database.

Of course pinba would not be superfluous, but there are several reasons why it is not on every project.

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danikin April 25, 2019 at 12:03 PM

Citymobil — a manual for improving availability amid business growth for startups. Part 2

• Mail.ru Group corporate blog,
• High performance,
• System Analysis and Design,
• Start-up development,
• Product Management

This is a second article out of a series «Citymobil — a manual for improving availability amid business growth for startups». You can read the first part here. Let’s continue to talk about the way we managed to improve the availability of Citymobil services. In the first article, we learned how to count the lost trips. Ok, we are counting them. What now? Now that we are equipped with an understandable tool to measure the lost trips, we can move to the most interesting part — how do we decrease losses? Without slowing down our current growth! Since it seemed to us that the lion’s share of technical problems causing the trips loss had something to do with the backend, we decided to turn our attention to the backend development process first. Jumping ahead of myself, I’m going to say that we were right — the backend became the main site of the battle for the lost trips.

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danikin April 22, 2019 at 06:52 PM

Citymobil — a manual for improving availability amid business growth for startups. Part 1

• Mail.ru Group corporate blog,
• High performance,
• System Analysis and Design,
• Start-up development,
• Product Management

In this first part of an article series «Citymobil — a manual for improving availability amid business growth for startups» I’m going to break down the way we managed to dramatically scale up the availability of Citymobil services. The article opens with the story about our business, our task, the reason for this task to increase the availability emerged and limitations. Citymobil is a rapid-growing taxi aggregator. In 2018, it increased by more than 15 times in terms of number of successfully completed trips. Some months showed 50% increase compared with the previous month.

The business grew like a weed in every direction (it still does): there was an increase in server load, team size and number of deployments. At the same time the new threats to service availability emerged. The company faced a task of the most importance — how to increase availability without compromising company growth. In this article, I’ll talk about the way we managed to solve this task in a relatively short time.

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t1ha = Fast Positive Hash

• High performance,
• Perfect code,
• C

• From sandbox

The authoritative guide to Blockchain Sharding

• High performance,
• Distributed systems,
• Cryptocurrencies

katiem January 17, 2019 at 12:55 PM

Gotta Go Fast: Building for Speed in iOS. Part 2

• e-Legion corporate blog,
• High performance,
• Development for iOS,
• Development of mobile applications,
• Swift

Sometimes you can find yourself in a situation where your app cannot perform well. So here are some instruments you can use and best practices you can implement to make things better.

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katiem January 17, 2019 at 12:54 PM

Gotta Go Fast: Building for Speed in iOS. Part 1

• e-Legion corporate blog,
• High performance,
• Development for iOS,
• Development of mobile applications,
• Swift

There are a lot of tips and tricks that allow iOS developers to know how to make performance optimizations to get animations in applications run smoothly. After reading the article you will realize what 16.67 milliseconds for iOS developer means, and which tools are better to use to track down the code.

The article is based on the keynote talk delivered by Luke Parham, currently an iOS engineer at Apple and an author of tutorials for iOS development on RayWenderlich.com, at the International Mobile Developers Conference MBLT DEV 2017.

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datacompboy January 15, 2019 at 04:15 PM

What to think during NALSD interview

• Google corporate blog,
• High performance,
• System Analysis and Design,
• IT career,
• Distributed systems

There are a lot of posts about what a typical coding interview at Google looks like. But, while not as widely described and discussed, there is also quite often a system design interview. For an SRE position it’s NALSD: non-abstract large system design. The key difference between SWE and SRE interviews consists in these two letters: NA.

So, what is the difference? How to be prepared for this interview? Let’s be non-abstract, and use an example. To be more non-abstract, let’s take something from the material world, such that you won’t be asked the exact same thing at the real interview (at least, not at the Google interview) :)

So, let’s design a public library system. For the paper books, like you have seen everywhere around. The whole text below was written all at once within around one hour, to roughly show you the areas that you should be able to cover / touch during the interview. Please excuse some disorder, that’s how I think (therefore I am).

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