Hi, "Dittmar, Daniel" wrote: > > > I want to use SAP DB for 4 separate internal applications - > > now I have to > > make the decision of using 4 DB-instance or using 1 instance with 4 > > different users. > > I would prefer using 4 instances because in that way I can > > make separate > > backups - and recoveries if necessary. > > The main drawback of having multiple instances is that the main ressources > (sessions, memory) can't be shared across instances. So you'll have to configure > each instance for the maximum expected load instead of configuring one instance for > the maximum combined load of all applications. > > Distributing I/O over the disks doesn't work as well as in a single instance because > the instances will happily write to the same disk at the same time (probably not a > real problem when using RAID). > > SAP DB tries to match the number of running tasks to te number of CPUs. This is not > possible with multiple instances because you could > - restrict the numbers of CPUs per instance, thus having possibly idle CPUs > - let the instances compete for all the CPUs, which is less efficient because of > additional context switches,
on the other hand Backup and Recovery scenarios are much easier for multiple instances. There you can save the components individually with the fast standard backup and restore routines. If you use multiple users and you want to backup and recover users (components) individually, you have to use the extraction routine of the SAP DB loader and this is usually much slower than standard backups and recoveries. In some cases the multiple users solution can also be very usefull e.g. if you have components/users which depends on each other. Then you can save a scenario with one save and the consistency continue in the backups. You see, the decision is not very easy and has to be considered on what is most important for you. Ciao Ralf _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
