I just found the time to run our MassIndexer against Hibernate 6.2.0CR2. Performance is significantly better than 6.1.6, but it is still a lot slower than 5.6.15:

Hibernate 5:

INF MassIndexerImpl Finished updating index in 337s.

Hibernate 6.1.6:

INF MassIndexerImpl Finished updating index in 474s.

Hibernate 6.2.0CR2:

INF MassIndexerImpl Finished updating index in 417s.

I’m guessing that most of the additional overhead still comes from fetching entities with associations as documented in the simple performance test in my PRs.