Gather real-time stats when UPDATE stmt uses index scan.
Rediscovery Notes
Given an update stmt with index scan, real-time stats should be gathered.
Workaround
alter session set "_optimizer_gather_stats_on_conventional_dml" = false;
Please note: The above is a summary description only. Actual symptoms can vary. Matching to any symptoms here does not confirm that you are encountering this problem. For questions about this bug please consult Oracle Support.
References
Bug:29457502 (This link will only work for PUBLISHED bugs) Note:245840.1 Information on the sections in this article