Hey Tim -
Just so I'm clear - did you have this working in 7 and it was faster? You said "Has anyone had that problem since T8 has been released", so I'm not sure if I'm reading into things too much, or if you had something that worked in 7 and now is slow in 8...
Well, in Tableau 7 blending was a lot more restricted, but when data was blended, it was quicker.
Now in Tableau 8, the restrictions are gone, but the blending is taking a lot longer. I guess it's not apples and oranges, but...
In T8, what I'm trying to do is (since I work with one table that's about 100+MM rows)
Relationship = B.customer_account_id = A.customer_account_id
When I blend the tables together to show A.clicks by B.customer_settings, it takes so long that the process times out. Granted as I mentioned, Table A = 100MM rows and Table B = 1.5MM rows. The problem is also joining at source means that I now have a 100MM row table that has 9 columns instead of 6, with data that I might not necessarily need regularly.
Maybe some advice on blending this level of data might help
How many unique values are present in your linking fields? If there are a very large number of unique values (>50,000) then some of the slow performance may be simply due to moving around a large amount of data over the network. Tableau typically works with large data sets by pushing queries to the database, where they can execute quickly and return relatively small result sets due to aggregation and filtering. However operations like creating an Extract or using Data Blending may require moving much more data than typically found in a query result set.
We hope to provide more details about the performance and behavior of Data Blending in a future whitepaper or KB article, but I can't commit to a timeframe for this effort.
In the meantime, I'll also suggest that you experiment with updating your MySQL ODBC driver to version 5.1 or newer. While Tableau still lists the v3.51 MySQL ODBC driver as the official one, I believe that we have made improvements to the MySQL connector in Tableau 8.0 that allows it to work with newer MySQL driver versions. In particular this may make it easier for you to work with complex joins or Custom SQL without experiencing the problems you described. Don't count this as official word until you see that we have updated our Drivers page, but you may find it to be a useful experiment in the near term. Here's the official Drivers page for reference: http://www.tableausoftware.com/support/drivers
I hope this helps,