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 in a “ClickHouse way.”
Even now, ClickHouse updates are asynchronous, which makes them difficult to use in interactive applications. Still, in many use cases users need to apply modifications to existing data and expect to see the effect immediately. Can ClickHouse do that? Sure it can.Read More
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 or as of the same day yesterday and so on. Financial market data analysis and all sorts of monitoring applications are typical examples.
Databases have different ways to achieve this task and ClickHouse is not an exception here. In fact, ClickHouse offers at least 5 different approaches. In this article, we will review and compare them.Read More