之前对选Release、Patch Set、PSU都有专门的文档，现在早已简化，针对这些以及之后RU、RUR等都包含在MOS文档：2118136.2
- Assistant: Download Reference for Oracle Database/GI Update, Revision, PSU, SPU(CPU), Bundle Patches, Patchsets and Base Releases (Doc ID 2118136.2)
我们根据需求就可以方便选择对应介质下载。比如下载19.x RU补丁，就点选如下：
注意需下载最新匹配的OPatch用来打补丁；可以搜索下面文章ID，有对应下载链接
- How To Download And Install The Latest OPatch(6880880) Version (Doc ID 274526.1)
2021-11-01 增订：
关于补丁，MOS文档：Oracle Database Patches to Consider for 19c (Doc ID 2781612.2) 给出了三个层次的逐步方法论：
1.先应用最新的季度RU补丁；
2.应用关键/推荐的One-off补丁；
3.针对某个特性/功能应用对应的补丁；
When applying Database patches, Oracle recommends that you take a 3-tiered step-by-step approach.
LEVEL 1: Apply latest quarterly patches:
Apply latest RU using Master Note for Database Proactive Patch Program (Doc ID 888.1)
Also review “Known Issues impacting the RU” (For example, Note 19202104.9 is the Known Issues note for the 19.11 RU.LEVEL 2: Apply Critical/Recommended patches:
For Exadata environments: Exadata Critical Issues (Doc ID 1270094.1)
For all Database customers: Oracle Database 19c Important Recommended One-off Patches (Doc ID 555.1)LEVEL 3: Apply additional patches based on features or focus areas:
Use the tabs in this document for quick access to additional feature based patches
其实这里面其实有几个关键常用且好记的MOS文档，比如888.1和555.1，非常方便索引对应补丁信息：
比如根据文档888.1，可以快速定位到补丁以及对应的已知问题，而且还有补丁对应的bug修复列表清单：
Primary Note for Database Proactive Patch Program (Doc ID 888.1) {
补丁的已知问题：{
Oracle Database 19c Release Update & Release Update Revision October 2021 Known Issues (Doc ID 19202110.9)
...
}
bug修复列表清单：{
Database 19 Release Updates and Revisions Bugs Fixed Lists (Doc ID 2523220.1)
Grid Infrastructure 19 Release Updates and Revisions Bugs Fixed Lists (Doc ID 2523221.1)
}
}
根据文档555.1，可以快速找到重点被推荐的One-off补丁：
- Oracle Database 19c Important Recommended One-off Patches (Doc ID 555.1)
此外，目前一体机的关键问题是有单独列出的一个文档，目前还没有类似888.1/555.1 这样好记的文档号：
- Exadata Critical Issues (Doc ID 1270094.1)
