In the current mass indexer, there're 2 parameters for different sizes:

• objectLoadingBatchSize: Sets the batch size used to load the root entities.
• idFetchSize: Specifies the fetch size to be used when loading primary keys if objects to be indexed.

In JSR-352, we use a single value (fetchSize) for both idFetchSize and objectLoadingBatchSize. See:

• org.hibernate.search.jsr352.massindexing.impl.steps.lucene.PartitionMapper.buildScrollableResults(StatelessSession, Session, Class<?>, Set<Criterion>)
• org.hibernate.search.jsr352.massindexing.impl.steps.lucene.EntityReader.buildScrollUsingCriteria(StatelessSession, PartitionBound, Object, JobContextData)

We may want to split them in the future.