DB2 Connect Enterprise Edition gateways now provide load balancing and fault-tolerance when routing connections to multiple SYSPLEXes. When connected to DB2 for OS/390 running in a data sharing environment, DB Connect will spread the workload amongst the different DB2 subsytems comprising the data sharing group, based on the system load information provided by the Workload Manager (WLM). This support requires DB2 for OS/390 Version 5.1.
Each SYSPLEX returns weighted priority information for each connection address, and this information is cached by DB2 Connect at the gateway, where it is used to balance connections by distributing them among the returned addresses, based on the returned priorities.
DB2 Connect gateways also provide fault-tolerance by trying alternate addresses in the event of a connection failure. An error will only be returned to the application if all known connections have failed. Since for SNA addresses there is no equivalent to Domain Name Server (DNS) lookup, in order to ensure that a connection can be made the first time after a db2start, DB2 Connect writes the addresses returned for SNA to the file db2con.ini, and this file is read on db2start. This provides a means to recover if the catalogued node is down.
In the event of failure to connect to a particular SNA address the following message is written to the db2diag.log:
DIA4805E A connection cannot be established to the DRDA application server at SNA address "%1" due to unknown symbolic destination name "%2".
A new profile (or registry) variable DB2SYSPLEX_SERVER has been created to enable this feature. If DB2SYSPLEX_SERVER is not present or is set to a non-zero value, then SYSPLEX exploitation is enabled. If DB2SYSPLEX_SERVER is set to zero then SYSPLEX exploitation is disabled. Setting DB2SYSPLEX_SERVER to a value of zero disables the SYSPLEX exploitation for the gateway regardless of how the DCS database catalog entry has been specified.