What is ClickHouse and How Does It Work? ClickHouse Database Explained

The internals of the ClickHouse database are of interest to many. In this blog, we answer questions related to ClickHouse and tell you what the ClickHouse database is and how ClickHouse works from the inside.

Introduction

If you‘ve heard of databases, you‘ve surely heard of ClickHouse. ClickHouse is an open-source Online Analytical Processing (OLAP) database that uses a column-oriented structure. The ClickHouse database is renowned for the fact that it can be used as a real-time data warehouse for a wide variety of applications spanning several use cases from identifying fraud and cybersecurity to analytics and gaming and that it‘s a true column-oriented DBMS. The ClickHouse database was built to be performant even under the most demanding circumstances – according to Alexey Milovidov, CTO at ClickHouse, the main purpose of the ClickHouse database was to filter and aggregate data in a blazing fast manner, but with the team making bits and pieces of small choices as time went by, the ClickHouse database quickly became the go-to database for developers, DBAs, and analysts alike.

The Architecture of ClickHouse

When we dive deeper into the ClickHouse database, we quickly notice that Alexey Milovidov didn‘t mince his words. The architecture of the ClickHouse database is behind years of thoughtful work and decisions that made ClickHouse both fast, performant, and easy to use. The ClickHouse database is fast because:

• The ClickHouse database is a column-oriented database management system: as such, the ClickHouse database is part of an elite group of database management systems that store data in columns, rather than in rows.
• The ClickHouse database is behind a smart architecture: some of the distinctive features of the ClickHouse database include the ability to compress data and provide different codecs for specific kinds of data, ClickHouse database is also designed to work on regular hard drives including anything from old hard disk drives to the newest generation NVMe drives.
• Processing queries in parallel: the ClickHouse database processes queries that are likely to utilize many resources in parallel while taking into consideration all of the resources available within your server. In other words, the more resources you have, the better, because the ClickHouse db will make use of them all. Multiple servers work too – since ClickHouse tolerates data residing on different shards, they can all be used to run queries in parallel, thus making SQL query performance even faster.
• ClickHouse‘s approach to SQL: ClickHouse also supports a query language based on SQL and supports many clauses originating from the original ANSI SQL standard. As such, the database is also a fit for users switching to ClickHouse from other database management systems.

How Does ClickHouse Work?

The architecture of the ClickHouse database is a big reason why the ClickHouse database is so quick. Percona even likens ClickHouse to analytic extensions for MySQL saying that when suitable hardware is in use, it‘s easy to understand why ClickHouse can execute millions of queries per second.

With ClickHouse being an analytic database that pairs with popular database management systems such as MySQL, ClickHouse can take off the load of MySQL‘s hands by:

• Removing the need for complex aggregation – one of the primary use cases of ClickHouse is to act as a real-time analytics database. As such, ClickHouse is able to reduce complex aggregation pipelines that burden your MySQL database such as the number of unique readers in a blog per day/week/month/year, the number of unique visitors on a website per day, etc. And helps you analyze and understand the data instead of drowning in it.
• Answering burning questions quickly and without issues – questions like „Why didn‘t the user #449482 complete a purchase on Monday and exit the application instead?“ need digging and understanding not only of how a database works but what makes the user perform certain actions, and OLAP databases are great at answering these questions. MySQL and many other relational databases are often slow when it comes to answering burning questions and as such, OLAP databases such as ClickHouse are often the first step towards an answer to these questions.
• Acting as a supplement for MySQL – the features of ClickHouse make it a suitable database for acting on aggregated data and working with multithreaded queries at the blink of an eye, which is something MySQL cannot be proud of. MySQL is a great database management system – but it does have limitations in certain spheres, which ClickHouse proudly overcomes.

Once we understand how the ClickHouse database takes off the load from many relational database management systems (see points above), we start to understand why the customers of ClickHouse include companies like CloudFlare, eBay, Microsoft, ServiceNow, Spotify, Lyft, NetApp, HubSpot, and others. Many companies using the ClickHouse database use its so-called „semantic layer“ to perform calculations and other things to facilitate a specific use case:

Summary

The ClickHouse database is an awesome OLAP database that‘s capable of assisting users in a variety of use cases ranging from real-time analytics to cybercrime and fraud prevention using machine learning and generative AI.

The team behind ClickHouse includes top-notch engineers from Netflix, Elastic, Tableau, GoDaddy, DoorDash, and even ex-product managers from Arctype – a SQL client that existed from early 2021 until fall 2022 when it was acquired by none other than the ClickHouse database itself. With the ClickHouse database having a rather short history (the company was incorporated in Delaware in 2021), we can‘t wait to see what the ClickHouse team has in store for the future.

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Frequently Asked Questions

What is ClickHouse?

The ClickHouse database is a fast OLAP and column-based databases that allows for the generation of real-time analytical reports with SQL queries.

What are the Primary Use Cases of the ClickHouse Database?

ClickHouse is primarily used for real-time data analytics, but it can also support observability, machine learning and generative AI, fraud and cybercrime detection, and many other use cases.

What Companies Use ClickHouse?

Companies using ClickHouse including CloudFlare, Hubspot, Vimeo, Microsoft, Lyft, and many others.