DB2 Connect Enterprise Edition servers 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, DB2 Connect will spread the workload amongst the different DB2 subsystems 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 or later.
Each SYSPLEX returns weighted priority information for each connection address, and this information is cached by DB2 Connect at the server, where it is used to balance connections by distributing them among the returned addresses, based on the returned priorities.
DB2 Connect Enterprise Edition servers 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, 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 server regardless of how the DCS database catalog entry has been specified.
The db2 registry variable DB2CONNECT_IN_APP_PROCESS can be used to allow clients running on the same machine as the DB2 Connect Enterprise Edition server to exploit the SYSPLEX support. For more information, refer to the DB2 Connect User's Guide.
With the addition of the concentrator, DB2 Connect now has the ability to balance the workload at transaction boundaries. The DB2 Connect concentrator must be enabled for this to work. Depending on the version of DB2 on the host, different granularity of load balancing will be achieved. If running against DB2 for OS/390 V6.1 of later, then on each transaction DB2 Connect will receive updated status from the WLM.
However, if the host is DB2 for OS/390 V5.1, then WLM status will still only be returned on a connect request. Because of this, long running connections are not recommended in conjunction with OS/390 V5.1 and SYSPLEX support. However long running connections can be used with OS/390 V6.1 and SYSPLEX support.