This raises many eyebrows. Why does the number of data sources impact my dashboard. And, I would say, it shouldn’t. And we have made many advancements where it might not.
However, in some of the older version prior to 10, we saw a direct co-relation between the number of data sources and the initial load time it took for a dashboard to load on the Tableau Server. If you are seeing that having a higher number of data sources is causing an issue, I would advise you to create dashboards that don’t use more than 3 data sources and compare it.
In any case, if you are combining more than 3 data sources for a single dashboard, I really think you should be using your enterprise data store (EDW or similar) to get the data so you aren’t combining data in real-time with data sources that are very different in terms of their technologies.
Another thing to consider is that Tableau makes separate connection to each one of the data sources so if you have 29 data sources to a database, Tableau might be doing some of the metadata work 29 times.