SAP Patching - Installing all OSS notes to the latest release level
SAP patching is the process of updating your current SAP system to the latest or newer patch level. Basically over time SAP releases numerous OSS notes which add various types of correction including fixing general problems, security flaws, legal requirements and improved functionality etc. Many of these you may or may not implement manually or via transaction SNOTE as you require them.
What SAP then does is at certain points in time, bundles all the new OSS notes since the last patch level into a new patch implementation level. This then allows you to patch your system and install all these OSS notes / SAP changes in one go. Sounds simple I here you say, well as long as you are running a 100% vanilla SAP system and you have not got OSS notes implemented which are ahead of the patch you are about to implement it probably will be. The extra work comes if you have made any changes to SAP standard code as you will need to ensure these are still valid and if so they are reapplied to the system after it has been patched.
A quick example to demonstrate this would be if you have added a section of custom code to an existing SAP program. When the patches come along it will over write these changes with the new version of the SAP code contained in the patch. You will then have to ensure these are re-implemented or confirm they are no longer required. This is also true if you have implemented the change via an enhancement point or standard SAP modification functionality. What if the section of code you added you enhancement point too changes significantly or disappears altogether, your correction may no longer be valid.
Don't worry too much though there are specific stages in the process and Sap transactions to use which help ensure this is as simple as possible. These tcodes include SPDD, SPAU, SPAU_ENH.
SAP SPDD stage
SAP SPAU stage
SAP SPAU_ENH transaction