Leave files untouched when changes only affect the database

[amogus07]

I use syncthing to sync my music library between my laptop and the micro sd in my phone. I noticed that whenever something related to an item is updated in the database, the 'modified' timestamp changes, even though nothing was modified. This meant that e.g. after the migration from genre to genres, pretty much every file was "modified", causing syncthing to overwrite every single file on my phone with a seemingly identical one, the only difference being the modified timestamp. Since my library is over 200GB, depending on how many files are affected, it can take multiple days till syncthing finishes syncing. I'd also imagine it's not good for my micro sd when every single file gets unnecessarily rewritten every now and then. Also, beets sometimes "hallucinates" changes when there are none. I don't know how to reproduce this reliably, but maybe someone else experienced similar issues too.

To summarize it, it seems like there are some issues with the comparison logic in beets that checks if a file actually needs to be modified.

[snejus]

Specifically for the genre -> genres migration, this was expected! For example, in FLAC files, you previously had:

GENRE=techno; rock

but after the migration this flac file now has

GENRE=techno
GENRE=rock

In this case, every file that contains a genre was 'rewritten' simply because the storage mechanism was updated.

The same should have happened for the rest of list level migrations: arrangers, composers, lyricists and remixers.

This otherwise does not happen in practice.

[amogus07]

ok, that was a bad example then, a better one would be running something like beet mod -a data_source:=MusicBrainz data_source=MusicBrainzPseudoRelease

[snejus]

beets does not rewrite files in such case.

[amogus07]

yes it does

[snejus]

Can you run the above modify command followed with beet write, and list file modification times before and after?

[amogus07]

beet mod -aW data_source:=MusicBrainz data_source=MusicBrainzPseudoRelease && beet write does not rewrite any files (I tested it with a query that only matches one file)

[snejus]

Sounds about right.

yes it does

In which case does it do so then?

[amogus07]

As I said, when running it without -W

[snejus]

Ah yes, it indeed seems to modify the file:

$ lsn /mnt/music/Music/alliance/oton_bsides/04_double0seven.flac
-rwxr-xr-x 1 sarunas sarunas 53M Apr  3 10:04 /mnt/music/Music/alliance/oton_bsides/04_double0seven.flac
$ beet mod -w path::/mnt/music/Music/alliance/oton_bsides/04_double0seven.flac data_source=bandcamp
Modifying 1 items.
56843 | 2023 / B-SIDES: OTON - Double 0 Seven
  data_source: musicbrainz -> bandcamp
Really modify, move and write tags? (Yes/no/select) y

$ lsn /mnt/music/Music/alliance/oton_bsides/04_double0seven.flac
-rwxr-xr-x 1 sarunas sarunas 53M Apr 13 19:33 /mnt/music/Music/alliance/oton_bsides/04_double0seven.flac