Cache types

When performing queries, ClickHouse uses different caches to speed up queries and reduce the need to read from or write to disk. The main cache types are:

mark_cache — Cache of marks used by table engines of the MergeTree family.
uncompressed_cache — Cache of uncompressed data used by table engines of the MergeTree family.
Operating system page cache (used indirectly, for files with actual data).

There are also a host of additional cache types:

DNS cache.
Regexp cache.
Compiled expressions cache.
Vector similarity index cache.
Text index cache.
Avro format schemas cache.
Dictionaries data cache.
Schema inference cache.
Filesystem cache over S3, Azure, Local and other disks.
Userspace page cache
Query cache.
Query condition cache.
Format schema cache.

Should you wish to clear one of the caches, for performance tuning, troubleshooting, or data consistency reasons, you can use the SYSTEM CLEAR ... CACHE statement.

Fundamentals

ClickHouse concepts

Best practices