From official doc – 4.3.1
The default isolation level for that method is SERIALIZABLE, which is
quite aggressive: READ_COMMITTED would work just as well;
READ_UNCOMMITTED would be fine if two processes are not likely to
collide in this way. However, since a call to the create* method is
quite short, it is unlikely that the SERIALIZED will cause problems,
as long as the database platform supports it.