Tell about your experience with ClickHouse.

ClickHouse is a columnar DBMS optimized for analytical queries and processing large volumes of data in real-time. In my experience, I used ClickHouse to build an analytics system where high speed of aggregations and filtering across billions of records was required.

Pros:

• Very high read speed due to columnar storage and data compression.
• Support for scaling and replication.
• Flexible SQL-like query language.

Cons:

• Not suitable for transactional loads, as it does not fully support ACID.
• Limited support for data updates and deletions (mainly inserts and reads).

An example of a simple query to count events by day:

SELECT event_date, count(*)
FROM events
GROUP BY event_date
ORDER BY event_date

Overall, ClickHouse is excellent for OLAP tasks and monitoring systems.