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.