Last Update Feature

Last Update database extension

This feature keeps track of when data in the database last changed. Changed, in this case could be any update to the database. It could be an edit that changes something important like the name or just the count of how many edits are open for this artist. This feature is designed to allow us to add the following features to MusicBrainz:

• "Artist was last updated X days ago" display in the server.
• RSS feeds for artists, albums and labels. You could subscribe to feeds of your artists and see changes being made to their data in MB.
• HTTP caching, which would allow us to let Google index the site without costing us a lot of bandwidth.

Not all of these features will be implemented immediately. For the next release I foresee doing the first two items above.

When an entity (artist, release, track, or release event) in the database changes it should update the some related entities. What entities should propagate changes to other entities was a subject of much discussion. Poorly planned update rules could cause avalanche effects where one change could update nearly the whole database. To reach a compromise of too many updates and not enough updates we decided to never recursively propagate changes and we decided to not keep a last update field for tracks. When a track is updated, the update field for the releases it belongs to are updated, which we believe will give enough information to our users about what data changed.

Database changes

For this feature we added new tables: artist_meta, label_meta. These tables only contain an id column (with a foreign key to the artist/label tables) and a lastupdate timestamp. For releases (albums in DB speak) we added the lastupdate column to the albummeta table. (I can't wait to get the naming in the DB normalized).

Update rules

If an artist is changed, then update:

• releases (including VA releases). For each of these releases, update the related:
  • labels
  • artists (excluding the original artist)

If a release is changed, then update the related:

• labels
• artists

If a label is changed, then update the related:

• releases. For each release, update the related:
  • labels (excluding the original label)
  • artists

If a track is changed, then update the related:

• releases. For each release, update the related:
  • labels
  • artists (all track artists for VA releases)

If release event is changed, then update the related:

• releases. For each release, update the related:
  • labels
  • artists

If discid is changed, then update the related:

• releases. For each release, update the related:
  • labels
  • artists

Remember, only those updates shown above are made. The changes are never recursive.