MySQL使用什么文件系统？

Question

Does MySQL use fread, read, mmap, or another file system when saving database data to the disk on a Linux OS? Or is MySQL doing a test to see which one to use? This is not in reference to saving config data. I'm interested in the actual database, preferably InnoDB.

Thanks for any help.

Edit: To be more specific, I'm interested in the c/c++ source code in MySQL that does the actual calls that saves data to a InnoDB database. Possible options are fread, read, mmap, among others.

Answer 1

What file system does MySQL use?

The MySQL access method code (InnoDB, MyISAM, AriaDB and the rest) uses the native file system of the host volume on the host operating system. NTFS on Windows, ext4fs on U**X systems, etc. The competent platform ports use a variety of I/O techniques including memory mapping, scatter/gather and ordinary read and write system calls, and integrate with the file systems' journaling features. The exact techniques used depend on the kind of query, the access method, and the state of caches.

Pro tip: Don't worry about this for performance reasons unless your server is running on an old 32-bit 486 machine you found in a storeroom (or unless you have millions of users and billions of rows of data).

Answer 2

On Linux systems all POSIX fileystems will work. fread is a libc construct that will translate to underlying syscalls like read , mmap , write etc.

The read, mmap, write operations are implemented in a Linux VFS (virtual file system) layer before those map to specific operations in the filesystem code. So any POSIX filesystem will work with MySQL.

The only filesystem test I've seen in the MySQL code is a fallocate syscall which isn't implemented on all filesystems (especially when it was first added, its probably significantly available now). There is an implementation workaround when fallocate isn't available.