This final article completes our tour of array capabilities. We’ll survey functions for array map and reduce operations, demonstrating behavior and commenting on performance. This is an opportunity to dig further into lambdas, which are critical for using arrays effectively.
ClickHouse arrays combine neatly with GROUP BY aggregation. We show how arrays track sequences and offer a couple of ways to do funnel analysis.
ClickHouse is a polyglot database that can talk to many external systems using dedicated engines or table functions. In modern cloud systems, the most important external system is object storage. It can hold raw data to import from or export…
ClickHouse contributors regularly add analytic features that go beyond standard SQL. This design approach is common in successful open source projects and reflects a bias toward solving real-world problems creatively. Arrays are a great example.
Data backups are an inglorious but vital part of IT operations. They are most challenging in “big data” deployments, such as analytics databases. This article will explore the plumbing involved in backing up ClickHouse and introduce the clickhouse-backup tool for…
Our colleague Mikhail Filimonov just published an excellent ClickHouse Kafka Engine FAQ. It provides users with answers to common questions about using stable versions, configuration parameters, standard SQL definitions, and many other topics. Even experienced users are likely to learn…
Kafka is a popular way to stream data into ClickHouse. ClickHouse has a built-in connector for this purpose — the Kafka engine. This article collects typical questions that we get in our support cases regarding the Kafka engine usage. We…
Mutable data is generally unwelcome in OLAP databases. ClickHouse is no exception to the rule. Like some other OLAP products, ClickHouse did not even support updates originally. Later on, updates were added, but like many other things they were added…
A common use case in time series applications is to get the measurement value at a given point of time. For example, if there is a stream of measurements, one often needs to query the measurement as of current time…
Multi-volume storage is crucial in many use cases. It helps to reduce storage costs as well as improves query performance by allowing placement of the most critical application data on the fastest storage devices. Monitoring data is a classic use…
Dec 28, 2019Grafana is a popular tool to create dashboards of time series data. It features outstanding graphics, interactive displays that zoom in on data, and support for a wide range of data sources. It turns out that one of…
This article is a continuation of the series describing multi-volume storage, which greatly increases ClickHouse server capacity using tiered storage. In the previous article we introduced why tiered storage is important, described multi-volume organization in ClickHouse, and worked through a…
