[riku_iki]

> The two main knobs are

my experience is that those are not enough, multiple algorithms will just fail saying you hit max memory limit. There are many other knobs, for example: when to start external aggregation or sorting. For some cases I couldn't figure out setup and query just hits OOM without any ideas how to fix it.

[FridgeSeal]

How is your table setup? It’s plausible the on-disk/index layout is not amenable to the kinds of queries you’re trying to do.

What kind of queries are you trying to do? Also, what kind of machine are you running on?

[riku_iki]

Trivial example would be to run select count(distinct) from large table with high cardinality values: https://github.com/ClickHouse/ClickHouse/issues/47520