Host templates should not create multiple data sources

[billpitz]

I have a data template that uses a script to pull a large number of statistics from a proprietary application.

When a host template is used to create several graph templates for this data, a new data source is created (from the data template) for each graph. This defeats the purpose of the single data query -- which was to produce minimal load on the application being polled.

More details:
http://forums.cacti.net/about24292.html

This is a real limit to Cacti's scalability for custom data sources.