v.20.1Experimental Feature
Added Experimental Setting for mmap I/O to Read Large Files Efficiently
Added experimental setting min_bytes_to_use_mmap_io. It allows to read big files without copying data from kernel to userspace. The setting is disabled by default. Recommended threshold is about 64 MB, because mmap/munmap is slow. #8520 (alexey-milovidov)Why it matters
This feature aims to improve the efficiency of reading large files by leveraging mmap, which can reduce CPU overhead by eliminating the need to copy data between kernel and userspace. It is designed for large files (recommended threshold around 64 MB) because mmap and munmap operations can be slow for smaller files.How to use it
Enable the feature by settingmin_bytes_to_use_mmap_io to a desired threshold (in bytes) in the ClickHouse settings. For example, to enable mmap I/O for files larger than 64 MB, set min_bytes_to_use_mmap_io=67108864. The setting is disabled by default.