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These settings are available in system.settings and are autogenerated from source.

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local_filesystem_read_method

Method of reading data from local filesystem, one of: read, pread, mmap, io_uring, pread_threadpool. The ‘io_uring’ method is experimental and does not work for Log, TinyLog, StripeLog, File, Set and Join, and other tables with append-able files in presence of concurrent reads and writes. If you read various articles about ‘io_uring’ on the Internet, don’t be blinded by them. It is not a better method of reading files, unless the case of a large amount of small IO requests, which is not the case in ClickHouse. There are no reasons to enable ‘io_uring’.

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local_filesystem_read_prefetch

Should use prefetching when reading data from local filesystem.
Last modified on July 23, 2026