This weekend, Nov 3, 2019, most time zones will set time back one hour. However, this year, Brazil will not participate in the clock change, now or in the future.
For questions/official statements about the timezone change itself, please contact the Brazil Government. IANA has updated Time Zone Database to reflect this change (tzcode2019b.tar) http://www.iana.org/time-zones . This change is included in the database DST patch v34 Patch 29997937
The Database Support team has also put together several KM Notes to help you understand this change. The Oracle Kernel itself is not impacted by the OS/System clock changes (or for that matter Oracle DST patches) (See KM Note 1013279.6 How does Daylight Savings Time Affect the Database Kernel). However, columns and datatypes TSTZ and TSLTZ are affected.
See KM Note 2603532.1 Brazil No Longer Observes DST From November 2019 Onwards- Impact on Oracle RDBMS