Add C comment about why we throw an error if the pg_upgrade old/new
database counts don't match.
prep_status("Restoring user relation files\n");
+ /*
+ * If the user removed the 'postgres' database from the old cluster,
+ * this will cause the database counts to not match and throw an error.
+ * We could allow this to work because the new database is empty (we
+ * checked), but we don't.
+ */
if (old_db_arr->ndbs != new_db_arr->ndbs)
pg_log(PG_FATAL, "old and new clusters have a different number of databases\n");