SAP NetWeaver AS Java: High Availability 
This section describes the features of SAP NetWeaver Application Server (AS) Java for high availability. We describe the causes of downtime and the effects of such failures. We also describe how you can avoid or decrease downtime for SAP NetWeaver AS Java.
Note
This part of the documentation refers to SAP NetWeaver AS Java.
For more information about SAP NetWeaver technical infrastructure, see the Technical Infrastructure Guide: SAP NetWeaver <Release>, which you can find at:
http://service.sap.com/instguidesNW
You need to consider the database you are using to run SAP NetWeaver AS Java.
You need to consider planned downtime to change:
Applications
You can change applications while the system is online, which means that only the changed application is unavailable. All other applications remain available.
Services of SAP NetWeaver AS Java
You have to make such changes offline, which means that SAP NetWeaver AS Java is not available.