min_bytes_to_use_direct_io
The minimum data volume required for using direct I/O access to the storage disk. ClickHouse uses this setting when reading data from tables. If the total storage volume of all the data to be read exceedsmin_bytes_to_use_direct_io bytes, then ClickHouse reads the data from the storage disk with the O_DIRECT option.
Possible values:
- 0 — Direct I/O is disabled.
- Positive integer.
min_bytes_to_use_mmap_io
This is an experimental setting. Sets the minimum amount of memory for reading large files without copying data from the kernel to userspace. Recommended threshold is about 64 MB, because mmap/munmap is slow. It makes sense only for large files and helps only if data reside in the page cache. Possible values:- Positive integer.
- 0 — Big files read with only copying data from kernel to userspace.