Versions 11.2.0.4 and 12.1.0.2 or higher enable the databases to allow a higher current maximum SCN limit and so support a transaction rate which is many times higher than earlier releases. This way of working allows over 500 years of data processing for any Oracle Database. The maximum SCN limit is calculated at any point in time based on the number of seconds elapsed since 1988. However, the increased maximum SCN limit only becomes effective after June 23 rd 2019. The patches which need to be installed, make it possible to support increased maximum SCN limit. Why will this only happen after June 2019? Starting from version 12.1, one can find any incoming database links via a query on the DBA_DB_LINK_SOURCES view, which can save some time finding the existing database links between databases. For versions prior to 12.1 one should check the DB links via the DBA_DB_LINKS view and make the linking to check if patching will be needed or not. So this already makes it easier to determine the impact on your Oracle Database environment.

Database Links between an unpatched/old release database and a patched/newer version might encounter errors (for some cases) at any point in time, after June 23 rd.

However, it’s still recommended to upgrade to a higher version (for security purposes, for support, etc…).

Database Links between unpatched databases or between older releases are not affected by this change.

It’s even better to upgrade to 11.2.0.4 or higher (preferably 12c R2)

All 11g R1 (11.1) versions need to be upgraded/patched to at least version 11.1.0.7.20.

All 11g R2 (11.2) versions need to be upgraded/patched to at least version 11.2.0.3.9.Versions 11.2.0.4, 12.1.0.2 or higher and 12.2.0.1 or higher already include the fixes needed.

Oracle also released a note with additional information: 2335265.1 (“Recommended patching and actions for Oracle database versions 12.1.0.1, 11.2.0.3 and earlier – before June 2019”). On this date, changes in the maximum SCN limit will happen. In October 2018 there was an update: April 2019 has been replaced by June 2019 (“Recommended patches and actions for Oracle databases versions 12.1.0.1, 11.2.0.3 and earlier – before June 2019”), to be more precise, affected databases should be patched before June 23 rd 2019. Moreover, what about Oracle 10g R2 and older, those editions are not supported anymore so no additional patches will be released?

This caused some confusion for Oracle database users who thought that database links would not work anymore after April 2019 if no additional patch was installed. On February 15 th 2018 Oracle published note 2361478.1 (“Oracle Databases Need to be Patched to a Minimum Patchset/PSU/RU level before April 2019”), stating that database versions prior to 12.1.0.2 (except for 11.2.0.4) will need additional patching in order to be able to use database links after April 2019.

Oracle 10g to 12c upgrade