What is Write Back?

Question

When I process a cube in SSMS and script to XMLA, I notice the following element:

<WriteBackTableCreation>UseExisting</WriteBackTableCreation>

What is the writeback table creation feature, and what does it mean for SSAS to UseExisting?

Answer 1

WritebackTableCreation Element (XMLA):

Determines whether a writeback table is created during the Process operation...

UseExisting Use the existing writeback table, if one already exists. If one does not exist, an error occurs.

Also on Specifying Processing Options:

Writeback Table Options If writeback is enabled in the Analysis Services project, this setting defines how writeback is handled....

For more details, see Enabling and Securing Data Entry with Analysis Services Writeback:

Why would you want to write data back to Analysis Services rather than the relational database that provides the raw data? One reason is latency. When you write data back to a relational database, users have to wait until the cube is processed before the latest data becomes available in their reports. However, when you enable writeback, users can submit data straight into the cube in the current session, making it instantly visible to other users of the Analysis Services database

Answer 2

Check out this blog post, describes writeback and why it would create a table (or use an existing table):

http://bimatters1403.wordpress.com/2008/02/05/ssas-2008-molap-writeback/

Answer 3

Check out this blog post, too. It's a very good tutorial (step by step) to understand the writeback cube process: http://www.bibabos.com/microsoft-bi/microsoft-writeback-cube-simple-approving-concept/