I had a closer look, and it seems this feature is only effective if the MergePolicy implement findFullFlushMerges. None of the built-in merge policies do, and in particular the (non-configurable) merge policy defined by Hibernate Search doesn't. So, this setting is currently pointless, at least until we allow users to provide their own MergePolicy. Closing this for now. See org.apache.lucene.index.IndexWriterConfig#DEFAULT_MAX_COMMIT_MERGE_WAIT_MILLIS |