In SAP HANA SPS09 version, the feature multi-tenancy has been implemented. Multi-Tenant Database system means in a database management system where more than one database container (i.e. tenant database ) could be configured. The basic feature of a multi-tenant database system is to have one single System Database to handle super admin tasks and other tenant databases where business data from multiple clients could be stored isolated from each other. To have a better idea continue reading the article.
Before understanding multi-tenancy , we should know what it was earlier , before SPS09.
In earlier versions of SPS09, till SPS08, on the top of hardware using hypervisor (a Virtual Machine Monitor) more than one VM used to be configured and upon each of those VMs , depends upon clients demand , preferred OS and Database used to be installed. Suppose , an organization is dealing with data from two clients , one is XYZ and another one is ABC. Obviously, XYZ wants its own standalone database to use their application XYZ and schema for it, in the same way ABC wants their own for their application ABC. So, for this scenario, previously on top of Hypervisor two VM and OS needed to be installed. Inside first VM and OS , Database XYZ for the Application XYZ and inside second VM and OS, Database ABC for the Application ABC used to be configured. The following image could explain better.
With the inclusion of Multi-Tenancy feature , things have changed. Now one installation of SAP HANA instance is sufficient to contain and serve two clients. In default, a System Database would be setup along with the two databases for two clients XYZ and ABC. Both would be isolated , would not be mingled with each other, sharing same hardware resources and other SAP HANA system resources while having the isolation of data with each other.
Hardware resource usage is optimized better with the implementation of multi-tenancy. Ability of central configuration and administration through system database, no need of administrator for each set of database. There is no need of Virtualization overhead. Cost behind resources is reduced in the case of multi tenancy. Task overheads like backup, maintenance and recovery are reduced.
In a distributed system, the database containers could be stored across the nodes. As shown in the following picture, in Host 1, two tenant databases along with the system database are stored, while in Host 2 a copy of first tenant database along with system database copy and in Host 3 a copy of second tenant database along with system database copy are stored. Host 2 and Host 3 would be required while the primary host i.e. Host 1 will be down. This is an example scenario to explain how it could be configured across cloud nodes.
There is one major drawback , that is if these two clients specifically mention different OS or different version of SAP HANA instance for their business, in such scenario it should be configured as it was earlier. But, obviously, SPS09 and later versions have flexibility to choose both of them.