Database Reference
In-Depth Information
needs of a given organization, different strategies can be deployed to minimize the business
downtime. Strategies available vary from normal weekend scheduled downtime with either
resource minimized or downtime-minimized strategies all the way to advanced upgrade
technologies that support near zero downtime (NZDT). We will discuss these concepts in
the next section.
System Switch Upgrade
In a system switch upgrade, the upgrade program creates a target release shadow instance
(second instance) in parallel to the source release in the same database. The target release is
built during production operation of the source release, except for certain steps that require a
downtime. During downtime, the remaining steps are completed in the shadow instance and
the upgrade program switches the shadow instance with the target release as the production
system and deletes the source release. The key steps performed during downtime are: ap-
plication tables are converted during the PARCONV_UPG phase, the kernel is switched to a
newer level during KX_SWITCH_1 phase, and the EU_SWITCH phase executes the switch
to the new system. If incremental table conversion (ICNV) is used, tables are converted dur-
ing productive operation, further reducing the downtime. Over time, SAP has improved the
upgrade to a point where the underlying complexity is hidden during the process and the
downtime has been reduced significantly because of better technology, such as system
switch upgrades and better tools such as ICNV. We will discuss the details of different up-
grade tools in subsequent sections of this chapter.
Upgrade Strategy (Preconfiguration Mode)
The upgrade strategy is primarily based on availability of the resources and utilization of the
downtime minimization tools and techniques during the upgrade. The strategy is executed
based on one of the following preconfiguration modes delivered by SAP (
Table 25-1
).
