An SAP HANA
system includes multiple isolated databases and may consist of one host or
several hosts.
An SAP HANA system is identified by a single system ID (SID) and contains one
or more tenant databases and one System DB. System DB/Tenant databases are identified
by a SID and a database name. We can identify differences between System DB and
tenant database on the basis of tasks performed at the database level. We can
connect respective databases from HANA Studio, SAP HANA Cockpit and DBACOCKPIT
from an administration standpoint.
The SAP HANA XS advanced application server is a layer on top of SAP HANA that
provides the platform for running SAP HANA-based Web applications. It is an
integral part of the SAP HANA system.
A HANA system may consist of one host or a cluster of multiple hosts. which is
called a "multiple-host, distributed system, or scale-out system and
supports scalability and availability"
Server Architecture
An SAP HANA database consists of multiple servers/Services, for example,
a name server, index server, preprocessor server, and so on. The most
important Server is the index server. It contains the actual data stores and
the engines for processing the data and runs in every tenant database.
Only the system database runs the name server. The name server contains
landscape information about the system as a whole, including which tenant
databases exist. It also provides index server functionality for the system
database. The name server does not own information about the location of tables
and table partitions in tenant databases. Database-related information is
stored in the relevant tenant database catalogue.
Tenant databases require only their own index server. Servers that do not
persist data, such as the compile server and the preprocessor server, run on
the system database and serve all databases.
- ·
Set of database users
- · Database catalog
- ·
Repository
- ·
Persistence
- ·
Backups
- ·
Traces and logs
If the SAP HANA XS classic server is available, it runs embedded in the (master) index server of the tenant database by default.
Tenant Databases
SAP HANA supports multiple
isolated databases in a single SAP HANA system. These are referred to as tenant
databases.
A system always has exactly one system database, used for central system
administration, and any number of tenant databases (including zero).
All the databases share the same installation of database system
software, the same computing resources, and the same system administration.
However, each database is self-contained and fully isolated with its own:
Although database objects such as schemas, tables, views, procedures, and so on are local to the database, cross-database SELECT queries are possible. This supports cross-application reporting.
The System Database
The system
database is created during either installation or conversion from a
single-container system to a tenant database system. The system database
contains information about the system as a whole, as well as all its tenant
databases. It is used for central system administration.
A system has
exactly one system database. It contains the data and users for system
administration. System administration tools, such as the SAP HANA cockpit,
can connect to this database. The system database stores overall system
landscape information, including knowledge of the tenant databases that exist
in the system. However, it doesn't own database-related topology information,
that is, information about the location of tables and table partitions in
databases. Database-related topology information is stored in the relevant
tenant database catalog.
Administration
tasks performed in the system database apply to the system as a whole and all
of its databases (for example, system-level configuration settings), or can
target specific tenant databases (for example, backup of a tenant database).
For more information, see Administration of Tenant Databases.
Things
to Remember About the System Database
- The system database does not have the same functionality as a tenant database.
- The system database is not a database with full SQL support.
- The system database cannot be distributed across multiple hosts, in other words, scale-out is not possible.
- If you need a full-featured SAP HANA database, you always have to create at least one tenant database.
- The system database does not support Application Function Libraries (AFL) and SAP liveCache applications.
- Cross-database access between the system database and a tenant database is not possible. The system database can show monitoring data from tenant databases (views in the schema SYS_DATABASES) but can never show actual content from tenant databases.
- The system database cannot be copied or moved to another host.
- SAP HANA options can only run in tenant databases.
- Tenant-specific configurations cannot be set in the system database. Only global settings are allowed.
- Features can only be restricted or disabled at a high level for tenant databases.