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Comment by spullara | Hacker News Reader

I ran into a problem like this with a service that used YAML for their config file. Basically when I edited it and saved the service would automatically pick up the change and load the config. However, the save hadn't completed so it only read a partial file which was still valid because, YAML.

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I still like XML and XSD. People look at me these days like I'm insane. But in this case a partially loaded XML document would not parse let alone pass schema validation.

Again vindicated. YAML needs to go away. It is misery. I'd rather have XSLT than Helm templates.

Both you and I are very aware that the XSLT + XML config file would have a tool for translating/generating it from a YAML; and most users would use that tool instead of configuring in XML.

Not if I amble around the office with a chair leg making menacing grunts they won't.

It's crazy how we still don't have the ability to atomically create/replace a file on the popular operating systems and filesystems , despite that being a super common use-case (without workarounds like renaming which have annoying limitations).

What would you want from an atomic replace of the contents of a file that rename() doesn't provide? Surely you've got to write the new contents somewhere before calling your atomic replace, and that's exactly what happens with rename/mv.

Rename does it and that it the workaround for issues like this.

How do you atomically replace an existing file using rename? I believe rename fails if the target file already exists, instead of atomically replacing it. Plus you end up with orphaned temporary files if you crash at the wrong point.

There is another workaround using unnamed tempfiles on Linux, but I think even that approach doesn't work for replacing files.

And then there is the issue that this creates a new file with the same name, instead of replacing the contents of the existing file. I think that's often not the desired behaviour regarding symlinks or inode ids.

And finally all those workarounds are overly complicated, so almost no application uses them, while pretty much every application that saves some kind of document (image, textfile, etc.) would benefit from atomic saving.

mv uses rename(). No issue with the target file existing beforehand. No issue with symlinks going stale, because they link to the name not the inode. Hard links will preserve the old file and still refer to that though (which is sometimes what you want, sometimes not). But for most, symlinks are far more common.

  $ echo "File 1" > file1
  $ echo "File 2" > file2
  $ ln -s file2 file3
  $ cat file3
  File 2
  $ echo "File 4" > file4
  $ mv file4 file2
  $ cat file3
  File 4

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