General observation with Plone 5.2 (and Python 3): ZODB commits are notoriously slow
I just reindexed ("Clear and rebuild") as small migration site with less than 100 objects. Reindexing time: one second, 10 seconds for the ZODB commit.
Similar experience with a production portal where we reindex some 300 objects per night (without updating the objects): takes about 3 seconds for retrieving and indexing the objects, 30 seconds for the commit.
That does not well right and is not consistent with the experience from the past.
Anyone with similar experiences?