The previous printing concept envisages a fixed assignment of an output device to a spool server. A spool server, on the other hand, can be assigned multiple output devices, which raises the risk of this server becoming overloaded. It would therefore be desirable to have a mechanisms for load balancing across multiple servers. Groups of spool servers are also advisable with regard to downtime security. Both aspects are taken into account by introducing logical spool servers.

A spool server is an SAP application server with at least one spool work process. Every output request is processed on a real spool server of this type.

An output device created in the SAP system can be assigned a spool server directly. However, there are many advantages associated with an additional logical layer between the output device and the spool server. You can use logical (spool) servers for this purpose, that stand for a hierarchy of other logical servers and/or real spool servers.

You can classify output devices and spool servers, for example, for test printing or production printing.

The SAP system checks the classifications when saving, and displays a warning message if there are deviations. For example, the system warns you if you attempt to assign a high volume printer to a production print server.

Creating a Logical Spool Server

You can maintain the spool server in transaction SPAD by choosing Spool Servers on the Devices / Servers tab page. Important information for a spool server:

Server Name

Name of the spool server, maximum of 20 characters long (case-sensitive). The field below the server name is intended for a short description.

Server Class

Classify the spool server here (for example, for mass printing).

Logical Server

Select this field when you create a logical server.

Mapping

Name of a real or logical server to which this logical server points.

You can define a spool server (real or logical) specifically for front-end printing by setting the profile parameter rspo/local_print/server to the server name. If no spool server is explicitly defined in this way, the local application server is used if this has at least one spool work process. Otherwise, one of the spool servers in the system defined in the system that has a minimal load is selected for the processing.

If you expect a significant workload due to front-end printing, you should configure at least one additional spool work process for each front-end printing spool server for other tasks.

As already mentioned, you can classify output devices and spool servers. To classify an output device, select it (in transaction SPAD under Output Devices) and call the path Edit -> Classification in the menu.

Advantages of Logical Spool Servers

Downtime Security

When creating a spool server (either a logical server or a spool server), you can specify an alternative server. If the normal server is not available, the SAP system attempts to use this alternative.

You must ensure that all printers that may be used by a different spool server can be controlled in the same way by every spool server. For example, if the output device Test 1 in the example points at operating system level to a printer P42 that is controlled locally, an operating system printer P42 must be available on servers twdf5000 and twdf5001.

You cannot store more than two spool servers for a logical server. Since a logical server can itself point to logical servers, extensive spool server hierarchies are also possible. You can display hierarchies of this type graphically using transaction SPAD.

Load Balancing

You can allow load balancing for every spool server with an alternative server (to do this, select the Allow Load Balancing field). The load of a spool server is calculated from the number of spool work processes, output requests, and printed pages.

For an output request for a spool server with load balancing (the setting can be made for logical servers and spool servers), the system determines the server with the lowest load. The algorithm is recursive: The same selection criteria are used on the mapping and the alternative server (both could be logical servers themselves).

Sequential request processing (property of an output device) has priority over the load balancing shown here (property of a spool server). This means that output requests for an output device with sequential request processing would not be distributed in accordance with the current load, although assigned to a spool server with load balancing.

Transporting the Print Landscape

The concept of logical servers supports you when defining a consistent, transportable print landscape. Logical servers can - unlike real spool servers - have the same name in various SAP systems. In this way, you can define a consistent SAP print architecture in the development system and then transport it to other systems. After the transport, you must only adjust the mapping of the logical servers to the spool servers of the new system.

There are functions for the manual transport of output devices and spool servers in transaction SPAD.