ClickHouse is the most natural choice for web analytics data.
This is distributed open source analytic DBMS with the focus on maximum query execution speed and storage efficiency.
It was initially created for Yandex Metrica - 2nd web analytics in the world processing ~100 billion records per day, 133 PiB of data in 120 trillion records in total.
Now ClickHouse used in countless applications including web analytics:
ClickHouse can be easily installed, starting from single node and scale up to thousands of nodes.
It can be easily embedded into self-hosted products. Examples: Sentry, PMM, etc...
There are two major issues I see:
The only way I can see a clickhouse integration even remotely possible in Matomo at the moment is by adding it as an optional plugin in Matomo that replaces one specific slow part of Matomo.
We looked into it a while ago and it does under circumstances work quite differently. AFAIK there were for example these two points:
It would mostly mean a rewrite of the tracking and archiving (report generation) part for ClickHouse