Tip #6: Preventing simultaneous executions of scheduled workflow

Let's assume you have n8n workflow which is managed by Google Sheet similar to the approach described in my previous posts Tip #2: Using Google Sheets as UI for your n8n workflow and Tip #5: Fixing Google Sheets quota exceeding issue. So you have big and dynamic amount of rows with different statuses and your workflow should automatically process with them accordingly.

In this case pretty good solution could be:

1. Scheduling workflow to execute at some small time intervals (i.e. every 5 minutes) so the maximum delay between your change in Google Sheet and workflow execution will be small enough.
2. Processing rows in a loop so one execution will process more than one row.
3. Updating Google Sheet right after each row processed so you will not loose previous rows data in the case of error.

So let's start from the workflow from Tip #5: Fixing Google Sheets quota exceeding issue:

Add Wait node with random wait amount to slow down execution a bit for demonstration purposes:

And also replace Manual Trigger node by Schedule Trigger node with trigger interval of 5 minutes:

So finally our workflow should look like this:

Now we are ready to execute our n8n workflow and see. At some point there are two concurrent executions which actually do the same job:

So the last thing to do is to set workflow timeout to the same value as scheduling interval:

Let's check again. Now we can see that there are no more concurrent executions:

And once the previous execution did some job, the next execution will continue with the row where the previous one was stopped:

So that's the idea to use scheduling and timeout with the same time interval. Works nicely!

You can find the template for the described approach here.

Tip #5: Fixing Google Sheets quota exceeding issue

Let's say you have Google Sheet and n8n workflow which works with it similar to the approach described in Tip #2: Using Google Sheets as UI for your n8n workflow. The only difference is that the volume of data is much bigger and you don't want to wait until all the data processed and update Google Sheet row by row instead. In this case you need to move the related Google Sheets node into the loop:

And add some more data to Google Sheet:

Let's execute it now. So it failed after processing of some number of items with the error message like "The service is receiving too many requests from you":

What we can do here? Let's use retry/delay approach described in Tip #3: Retry/delay more than 5 seconds/5 tries adding Wait nodes to error outputs of both Google Sheets nodes:

Wait amount can be 1 minute:

It's time to execute our workflow and see how it works:

Passed successfully. Also we can see that Wait node was executed 1 time so this approach works well.

Google Sheet for this tip is available here as well as n8n template.

Tip #4: Nested loops in n8n

Let's imagine you have some set of data like colors and you want to iterate over all of them. For illustration I will create this data set using Code node:

And after that I will add a Loop node:

After executing a workflow we can see 3 items in Done Branch as expected:

Ok, let's now imagine that we have some another data set like integer numbers and we also want to iterate over all of them in a nested loop. I will create another Code node for this:

And again I will add a nested Loop node:

And finally let's add Set node to a nested loop to show the current values of color and integer number:

The final workflow should look like this:

Now let's execute the workflow and check the results. What we can see is that outside loop's Done Branch has 18 items and the values are quite odd:

This is not we were expecting though. It looks like nested loops are not supported according to the comment of n8n team. But there is a workaround - let's move the body of outside loop to a separate sub-workflow:

It should have "color" input parameter:

And it also requires the change in Set node - we don't have outside loop here but have sub-workflow input instead:

Then get back to the main workflow and add Execute Sub-workflow node to call our sub-workflow with a nested loop:

Pass the color from the outside loop as an input parameter of sub-workflow:

It's time to test it. Let's execute the main workflow and check the results:

This is exactly what we were expecting to see. So for nested loops in n8n it's possible to use sub-workflow workaround.