说明：

在2019年4月之后没有把 数据库应该升级到提到的release/patchset/ PSU/BP levels (or above)时（包含10.2及11.1），当使用database link的时候，会遇到 run-time errors。

MOS 文章说明如下：

In this Document

APPLIES TO:

Oracle Database - Standard Edition - Version 11.1.0.7 to 12.2.0.1 [Release 11.1 to 12.2]
Oracle Database - Enterprise Edition - Version 11.1.0.7 to 12.2.0.1 [Release 11.1 to 12.2]
Information in this document applies to any platform.

PURPOSE

This support note provides additional info related to mandatory patching/upgrade of all supported releases of Oracle Databases to a minimum patchset/PSU level before  April 2019.

SCOPE

 The document is intended for all DBAs.

DETAILS

All supported releases of Oracle Databases need to be patched to a minimum patchset/PSU level before  April 2019 to ensure proper functioning of database links. This note only applies to Database Server installations and the interoperability of database clients with database servers is not impacted by this patch.

1. What are the minimum recommended patchset/PSU/BP/RU levels?

For all database releases prior to 12.2.0.1, ensure that all interconnected databases are in the below mentioned patchset/ PSU/BP levels or above:

In summary, 12.2.0.1 and higher releases, 11.2.0.4 and 12.1.0.2 patchsets have this fix included, while patches are available for 11.1.0.7 and 11.2.0.3 releases. If you have any other database server installations (e.g. 10.2.0.5, 11.2.0.2), you should upgrade such databases if you would like the older databases to continue using database links with newer versions of databases.

2. What is the timeline for moving to the minimum recommended patchset/PSU/BP mentioned?

All databases should be at the above mentioned release/patchset/ PSU/BP levels (or above) before  April  2019. 

3. What happens if the mandatory PSU / patchset is not applied?

If either the source or target database using database links is not patched/upgraded to the right patchset/PSU level, you may get run-time errors during database link operations after  April 2019. In order to resolve the errors, you would immediately need to patch/upgrade the databases. 

4. What about databases that are 10.2 or older, which are not listed in the table?

Please ensure that you don't have any database link (incoming or outgoing) between earlier versions of databases (e.g. 10.2) and the database releases/patches mentioned in this document (Under Sec 1. What are the minimum recommended patchset/PSU/BP/RU levels? ) as we don't plan to release patches for those unsupported versions of databases. If you continue to have such database links after  April 2019, you may get run-time errors during database link operations and you would need to disconnect those database links at that time.

5. How can I check the details regarding the dblinks to and from a database?

In order to identify database links, please review "Viewing Information About database Links" in Database Administrator's guide. 

Please note that outgoing db links from a database can be identified via DBA_DB_LINKS view for all database releases.

select * from dba_db_links;

For 12.1 and later releases, you can also find out about incoming database links via DBA_DB_LINK_SOURCES view.

select * from dba_db_link_sources;