During upgrade from Nexus 2.x to Nexus 3.x, Nexus 3 logs may report the following type of ERROR:
This looks like a problem where multiple ProcessChangesStep threads in Nexus 3 could be attempting to update the same npm package metadata for different tarballs. The concern is that some npm package metadata tarballs may be lost on upgrade to Nexus 3 when encountering this type of ERROR.
In the case of a proxy repository, does not appear to be serious. In the case of this happening with a hosted repository, this is considerably more serious.
In Nexus 3, edit ./bin/nexus.vmoptions
Add this new line at the end of that file and save:
This attempts to reduce the migration concurrency to avoid the problem of different threads trying to update the same record.
Restart the Nexus 3 migration using a completely empty karaf.data directory