A Magical Mystery Tour of the LowCardinality Data Type

A Magical Mystery Tour of the LowCardinality Data Type

Alexander Zaitsev

Mar 27, 2019

Many ClickHouse features like LowCardinality data type seem mysterious to new users.  ClickHouse often deviates from standard SQL and many data types and operations do not even exist in other data warehouses. The key to understanding is that the ClickHouse engineering team values speed more than almost any other property. Mysterious SQL expressions often turn out to be ‘secret weapons’ to achieve unmatched speed.

In fact, the LowCardinality data type is an example of just such a feature. It has been available since Q4 2018 and was marked as production ready in Feb 2019, but still is not documented, magically appearing in some documentation examples. In this article we will fill the gap  by explaining how LowCardinality works, and when it should be used.

ClickHouse Continues to Crush Time Series

ClickHouse Continues to Crush Time Series

Alexander Zaitsev

In our previous articles we demonstrated that ClickHouse — a general purpose analytics DB — can easily compete with specialized DBMSs for time series data: TimescaleDB and InfluxDB. There were, however, certain queries, pretty typical for time series, where ClickHouse seemed at first glance to be at a disadvantage. The most notable example is returning the latest measurement for particular device. We will take this query and demonstrate how ClickHouse advanced features, namely materialized views and self-aggregating tables, can  dramatically improve performance.

Updates and Deletes in ClickHouse

Updates and Deletes in ClickHouse

Alexander Zaitsev

Oct 16, 2018

It’s been two years already ago when ClickHouse development team published an excellent blog post “How to update data in ClickHouse”. In that old times ClickHouse supported only monthly partitions, and for mutable data structures, they suggested to use pretty exotic data structures. We were all waiting for a more convenient approach, and finally, it is there: ClickHouse now supports updates in deletes! In this article, we will see how it works.

ClickHouse Digest #1

Alexander Zaitsev

Activity in and around ClickHouse has dramatically increased recent weeks. Percona Live in Dublin, meetups in Bay Area and Berlin, new features, many new companies adopting ClickHouse — all that generate a lot of news and increase interest to ClickHouse further.

In this article I would like to highlight some ClickHouse recent news. Eventually we plan to publish a monthly ClickHouse news digest, so this is a test ball.

Migration to ClickHouse. Practical guide

Alexander Zaitsev

Author: Alexander Zaitsev, Altinity Co-founder

In this presentation, Alexander talks about his experience in migration company data to ClickHouce, shares the most important lessons they learned, and discusses the best application design practices for building a large-scale platform based on ClickHouse.

Migration to ClickHouse

Alexander Zaitsev

Oct 23, 2017   
ClickHouse is an excellent analytics database choice not just for startups but also for companies that have already invested significant amount of resources into their analytics solutions, but are not completely satisfied with the results. In this article we will discuss how and when companies consider the ClickHouse migration project, and what challenges they may expect. We do not disclose any names, but every example has a real world prototype. 

Building Multi-Petabyte Data Warehouses with ClickHouse

Alexander Zaitsev

Author: Alexander Zaitsev, Altinity Co-founder

Overview: At LifeStreet we needed to scale our real time ad analytics platform to multiple petabytes. When Yandex has released ClickHouse to Open Source we quickly realized its potential, and started our implementation project. It was a long way but it finally worked out great.

Webinar: Supercharge Your Analytics with ClickHouse

Webinar: Supercharge Your Analytics with ClickHouse

Alexander Zaitsev

Speakers: Vadim Tkachenko, Percona’s, CTO and Alexander Zaitsev, Altinity’s Co-Founder.

ClickHouse is a real-time analytical database system. Even though they’re only celebrating one year as open source software, it has already proved itself ready for the serious workloads.

ClickHouse New Releases and ChangeLog

Alexander Zaitsev

It took a while for Yandex to respond to numerous community requests regarding release notes. But finally it’s there. On August 21-st Yandex created a changelog file covering releases starting from 1.1.54245, and they keep it up to date so far.