See also Appendix F. "Additional SNA Performance Tuning Hints and Tips".
You should consider the following:
Increasing the data transfer block size (buffer, message, block, RU (Request Unit), frame, etc.) reduces overhead of data transmission over a period of time. In communication subsystems such as IBM Communications Server for OS/2 and Microsoft SNA Server the RUSIZE parameter controls the data transfer block size.
The SNA communication system compares the RU size of each partner and uses the smaller of the two RU sizes. You can start tuning with an RU size of 4KB and increase it if necessary. You may get the best performance by setting the RUSIZE and the RQRIOBLK (see "RQRIOBLK") to the same value.
All APPN-compliant platforms perform adaptive pacing. This means that you do not need to worry about pacing values. If you are using software that is not APPN-compliant (such as VTAM 3.4), you may want to set the values of pacing parameters.
The most important pacing values to DB2 Connect are the ones utilized at the APPL-APPL layer of the SNA protocol stack:
A higher pacing value generally improves the data transfer throughput and utilization of the transmission medium.
In NCP, the other pacing values found in other definitions are to prevent the NCP's resources from being overrun.
Performance depends on keeping connections active and running. For example, you should maintain the SNA connection until other factors (such as cost) become more important.
If network transmission time is a more important performance factor than CPU processing time, data compression might improve performance. You can use data compression only if it is supported by the communication products at both ends of the connection.
The tuning of your communications software can affect performance. For more information, see books such as SNA Server for AIX and SNA Server Gateway Performance Guide. (This book applies specifically to AIX systems, but the information in it may also be useful to other users.)
The following considerations relate to the hardware:
Performance improves with a faster transmission medium. For example, the following are some typical raw data transfer rates:
The data transfer rate is limited by the slowest transmission medium in the path to the DRDA server.
You should carefully plan the memory usage of the network adapter and communication controller. In addition, you should work with a network specialist to ensure that the controller has the capability to handle the extra traffic generated by DB2 Connect.
If data crosses from LAN to LAN, and from one SNA Network to another SNA Network, consider the travel time. Bridges, routers, and gateways will add to the elapsed time. For example, reducing the number of bridges that are crossed reduces the number of hops required for each request.
The physical distance between nodes should also be considered. Even if a message is transferred by satellite, the transfer time is limited by the speed of light (3 * 10**8 m/s) and the round-trip distance between the sender and receiver.
If the bandwidth of the network has been fully utilized, both the response time and the data transfer rate for a single application will decrease.
Congestion can occur in the network when data accumulates at a particular part of the network; for example, at an old NCP with a very small buffer size.
If the error rate of the network is high, the throughput of the network will decrease and this will cause poor performance because of data re-transmission.