Clickhouse: LowCardinality is not documented

[simPod]

I checked docs on LowCardinality but cannot find any except some mentions in changelog. So I'm creating this issue to keep track of it.

[jelharou]

The Altinity blog is a great place to start: https://www.altinity.com/blog/2019/3/27/low-cardinality

[simPod]

Thanks for the link, already found this one and some others. But documented, it should be ;) From discussions I found here I understand it's production ready.

[blind-oracle]

From discussions I found here I understand it's production ready.

I wouldn't be so sure.

In some queries (like SELECT ... FROM ... WHERE low_card_column IN (...a lot of strings...) I found it to be 100s times slower than normal String. I've checked in CH 19.5, maybe it has improved, but I wouldn't count on it.

[alexey-milovidov]

@BayoNet I cannot find LowCardinality in documentation.
LowCardinality feature is used in production since long time ago.

[BayoNet]

Ok. I'll do it ASAP.

[simPod]

https://clickhouse.tech/docs/en/sql-reference/data-types/lowcardinality/