comm_bandwidth - Communications bandwidth configuration parameter
This parameter helps the query optimizer determine access paths by indicating the bandwidth between database partition servers.
- Configuration type
- Database manager
- Applies to
- Partitioned database server with local and remote clients
- Parameter type
- Configurable Online
- Propagation class
- Statement boundary
- Default [range]
- -1 [-1, 0.1 - 100000]
A value of -1 causes the parameter value to be reset to the default. The default value is calculated based on the speed of the underlying communications adapter. A value of 100 can be expected for systems using Gigabit Ethernet.
- Unit of measure
- Megabytes per second
The value calculated for the communications bandwidth, in megabytes per second, is used by the query optimizer to estimate the cost of performing certain operations between the database partition servers of a partitioned database system. The optimizer does not model the cost of communications between a client and a server, so this parameter should reflect only the nominal bandwidth between the database partition servers, if any.
You can explicitly set this value to model a production environment on your test system or to assess the impact of upgrading hardware.
Recommendation: You should only adjust this parameter if you want to model a different environment.
The communications bandwidth is used by the optimizer in determining access paths. You should consider rebinding applications (using the REBIND PACKAGE command) after changing this parameter.