In the DBA_TAB_MODIFICATIONS table, change statistics for all changed tables in the database are stored. The same information can also be accessed from the ALL_TAB_MODIFICATIONS table.
Because of the bug related to UNION ALL numbered 13984324, the records are not returned from these tables. The related bug is seen in the databases 188.8.131.52, 184.108.40.206 and 220.127.116.11. This bug has been fixed in versions 18.104.22.168 and above.
This problem can be fixed by applying a patch to the bug. Also, if we set the value of “_optimizer_join_factorization” parameter to “false” as workaround, the problem will be solved.
You can change the parameter as follows.
SQL > alter system set "_optimizer_join_factorization"=false scope=both sid='*';