On Wed, Jan 21, 2009 at 12:37:11PM +0000, Jamie Lokier wrote: > > What about btrfs with data checksums? Doesn't that count among > data-retrieval metadata? What about nilfs, which always writes data > to a new place? Etc. > > I'm wondering what exactly sync_file_range() definitely writes, and > what it doesn't write. > > If it's just in use by Oracle, and nobody's sure what it does, that > smacks of those secret APIs in Windows that made Word run a bit faster > than everyone else's word processer... sort of. :-) Actually, I take that back; Oracle (and most other enterprise databases; the world is not just Oracle --- there's also DB2, for example) generally uses Direct I/O, so I wonder if they are using sync_file_range() at all. I do wonder though how well or poorly Oracle will work on btrfs, or indeed any filesystem that uses WAFL-like or log-structutred filesystem-like algorithms. Most of the enterprise databases have been optimized for use on block devices and filesystems where you do write-in-place acesses; and some enterprise databases do their own data checksumming. So if I had to guess, I suspect the answer to the question I posed is "disastrously". :-) After all, such db's generally are happiest when the OS acts as a program loader than then gets the heck out of the way of the filesystem, hence their use of DIO. Which again brings me back to the question --- I wonder who is actually using sync_file_range, and what for? I would assume it is some database, most likely; so maybe we should check with MySQL or Postgres? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
