When a TREX system
is connected to an SAP system, both systems communicate with each other
through an RFC connection.
More than one
communication partner is involved in an RFC connection. The SAP system first
sends its requests to an SAP gateway. The SAP gateway forwards the requests to
a TREX RFC server. The TREX RFC server forwards the requests TREX-internally.
The graphic below depicts this.
There are different
types of RFC connections. To connect a TREX system, the system supports the
Registration activation type. With this activation
type, one or more TREX RFC servers register with the SAP gateway and maintain
a constant connection to it.
With regard to the
SAP gateway, there are two variants:
●
Communication takes
place using the local SAP gateway of the application server.
●
Communication takes
place using a central SAP gateway.
Local SAP Gateways for the Application Servers
With this variant,
each application server sends the requests to its local SAP gateway. On the
TREX side, TREX RFC servers are registered with each local SAP gateway. The
TREX configuration depends on the structure of the SAP system. In addition,
you must distinguish between TREX RFC servers in single-thread mode and those
in multithread mode during configuration:
TREX RFC Servers in Single-Thread Mode
In the case of TREX
RFC servers in single-thread mode, there are at least as many RFC servers
(instances/processes) running on each TREX host as there are application
servers. Each RFC server instance connects itself through a SAP gateway that
runs locally on each application server. The graphic below depicts
this.
TREX RFC Servers in Multithread Mode
In the case of TREX
RFC servers in multithread mode, exactly one RFC server (instance/process)
runs on each TREX host and within this one RFC server, at least as many
threads are started as there are application servers. The graphic below
depicts this.
The
multithread mode is recommended for the TREX RFC server. A single RFC server
instance that starts more than one thread in multithread mode consumes less
memory than many RFC server instances in single-thread mode. (For details of
the configuration, see Changing the Number of
RFC Server Instances or Threads). In the case of an initial TREX
installation, the TREX RFC server is configured for multithread mode by
default so you do not have to make any changes.
The TREX
configuration depends on the structure of the SAP system. Each TREX host runs
at least as many TREX RFC servers as there are application servers. If
application servers are added to or removed from the SAP system, you must
change the TREX configuration.
In the case of a
distributed TREX system, each TREX host is connected to each application
server in the SAP system. The graphic below depicts this.
Using the local SAP
gateways has the following benefits:
●
The local SAP
gateways process the requests quicker then a central SAP gateway.
●
The SAP gateway is
not a single point of failure. If an application server and its local SAP
gateway fail, the requests are distributed among the remaining application
servers and still continue to reach the TREX system.
Central SAP Gateway
The TREX
configuration does not depend on the structure of the SAP system. If
application servers are added to or removed from the SAP system, there is no
impact on the TREX configuration.
The disadvantage of
this variant is that the central SAP gateway is a “single point of
failure.” If it goes down, the connection between the SAP system and the
TREX system is unavailable.
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