Multiple, unconnected Block Until Done Tools

[PatrickB89]

Hi,

I have a question about the block until done tool. I often have the problem of writing in multiple sheets in the same excel file. My usual approach is the one described here:

https://community.alteryx.com/t5/Alteryx-Designer-Knowledge-Base/How-to-write-to-multiple-tabs-separ...

But I've seen some collegues of mine solving it like this:

My opinion is, that this is not how the tool works. But unfortunately (?) it does work. The order is ignored, but the streams behind the block until done tools are never run through at the same time. I was not able to build a workflow where this lead to the usual "Could not open file"-error. 

Is this just random, or will this always work? Can anyone provide an example where this does NOT work (except from workflows where the order actually matters)? Otherwise, this would be an easy workaround for problems with multiple inputs etc.

Thanks in advance,

Patrick

[PhilipMannering · Accepted solution]

It does seem to be the case that if two branches have two different Block Until Done tool then the one that was dropped first will be carried out in it's entirety before the second branch continues - this is news to me.

So it goes

1. Order of Block Until Done Tools

2. Order of Nodes within each Block Until Done tool.

The Output messages in my attached example shows this quite well.

In my experience, it's only when you're writing a lot of data to the same file with no Block Until Done tools that you get the "could not open file" error.

[PatrickB89]

Thanks for your reply!

So you think that this behaviour is reproducable?

Many of the workflows I see are based on inputs of variable size, and I don't want them to return errors in some cases (e.g. very big inputs). If the block until done tools are always working like in your proposed order, that problem can't occur. Since these workflows will be used by many users in my company, I want to be sure.

You are right, in most of the cases the 'could not open file' error occurs on big datasets, but I've seen it happen with very small sets as well and I don't want to rely on "It usually works" 😉

[CharlieS]

I think this happens to work because of the ToolID values. ToolIDs are assigned when a tool is added to the canvas and lower values (tools placed first) would be processed first. In the hierarchy of processing order in Alteryx, ToolID is very low (if not last). In other words, if the order is important: it should be designed in such a way to reflect that. Otherwise, if some tools are deleted and re-pasted into the canvas while working on the module, this will assign them new ToolID values. 

The Alteryx engine will also change the processing order for efficiency gains. @Ned mentions this here:

https://community.alteryx.com/t5/Alteryx-Designer-Discussions/How-to-control-the-order-of-components... 

This could be a reason why different file sizes will change the order. Perhaps the engine is estimating resource allocation and makes changes to optimize based on the data stream and/or available resources. 

I suggest that if the processing order is important, the workflow should be designed to reflect that with tool connections. 

[PatrickB89]

Ok, understood, thanks!

I think this behavious should be documented somewhere in the instructions, because it can be really userful in some cases.