Yes, I know.
My idea is not at all about individual updates of metadata columns; I'd simply add an information about the over-all version number of the metadata.
Here is my usage scenario:
I have a site which can be viewed via different hostnames, and the visible contents of some folders vary slightly, depending on the hostnames.
Some objects are visible in all hostnames, some only in a subset.
Now I change something about the metadata which is used by the public views of those folders; in my upgrade step, it is perfectly sufficient to update the metadata of the objects listed there.
Without the metadata_version information, I'd
- seek all objects for the first hostname,
- update their metadata,
- and when seeking the objects for the next hostname, I'd update the metadata again; but most objects have been updated before.
With the metadata_version at hand, I'd be able to skip the previously-updated objects easily.
Perhaps it turns out the metadata calculation effort really doesn't matter.
No problem: stop using it, and delete that column.
But perhaps it does make a difference; it depends, I'd say.