RFC-1323 Window scaling

 

Window scaling is supported on all Windows®, Linux™, and UNIX® platforms that support the RFC-1323 extensions for TCP/IP. You can enable this feature on DB2® for Windows, Linux, or UNIX using the DB2 registry variable DB2SORCVBUF. To turn window scaling on, this registry variable should be set to any value above 64K. For example, on DB2 for Windows, Linux, or UNIX, you can issue db2set DB2SORCVBUF =65537.

The maximum send and receive buffer sizes are dependent on the specific operating system. To ensure that buffer sizes configured have been accepted, the user can set the database manager configuration parameter DIAGLEVEL to 4 (informational) and check the administration notification log file for messages.

For window scaling to take effect it must be enabled on both ends of a connection; on both the workstation and the host, either directly through the operating system TCP/IP stack, or indirectly through the DB2 product. For instance, for DB2 for z/OS®, window scaling can currently only be activated through the operating system by setting TCPRCVBUFRSIZE to any value above 64K. If you are using a remote IBM® data server client to access a host or System i™ DB2 database through a DB2 Connect™ server workstation, you can enable window scaling on the client as well. By the same token, you can also enable window scaling between a remote IBM data server client and a workstation DB2 server when no host or System i DB2 database is involved.

While window scaling is designed to enhance network performance, it is important to note that the expected network performance improvement does not always materialize. Interaction among factors such as the frame size used for the ethernet or token ring LAN adapter, the IP MTU size, and other settings at routers throughout the communication link could even result in performance degradation once window scaling has been enabled. Therefore, by default, window scaling is disabled with both the send and receive buffers set to 64K.

You should be prepared to assess the impact of turning on window scaling and perform any necessary adjustments to the network. For an introduction to tuning the network for improved network performance, refer to http://www.networking.ibm.com/.

Parent topic: DB2 Connect tuning