I was wondering if there was a good pattern to trigger a second flow (using the next_page token as a parameter) from a task?

Hey @Jacques - for paged API’s we have a LOOP operator. You could use it to collect all your data in one task, then return the list of results, and use a

map

operator to process them in parallel.

I've implemented that, but as it turns out, that means we can't start transforming until we've fetched all the pages.

That’s true - if its possible to get a stable API URL for each page, then you could have a single task generate all of the URLs (or URL parameters), and then return that list. Then you could have a task that loads the data from that URL in a map, followed by another task that processes the item retrieved by the previous task. At the moment, Prefect maps are breadth-first but we will be releasing a depth-first enhancement very soon. That would look something like:

with Flow("test"):
  all_urls = retrieve_all_urls()
  load_result = load_data.map(all_urls)
  transform_data.map(load_result)

Unfortunately the API is unstable.

Ah ok. In that case, back to your original question, if you are using Prefect Cloud or the local server you could register another flow to process data and then kick it off with the GraphQL API or the

prefect.client.Client.create_flow_run()

method, passing your payload to the flow as a parameter. We don’t usually encourage this as a first cut because you lose a little visibility since your work is spread across multiple flows, but it may solve the issue and sometimes thats more important 🙂

Currently we are just using core, second option there makes sense, actually just trigger the second flow from task directly

👌 give it a shot in the local server or with the free tier of Cloud and let us know!

Just thinking about this it's almost like we want something like a "meta flow", something that can link flows together.

Yeah, this is something we grapple with a lot - the use cases are clear but the complexity it introduces can be enormous, so we are working to find an appropriate API

Nice, hope you figure it out, if you can do it as cleanly as the rest it would amazing.

Ha, thanks!

Yeah I've been experimenting with running the dask local executor in lambda and just run it sort of self contained so we can easily move bits from lambda to fargate as they grow - you have any comments about using dask local in prod?

Only that we think dask is awesome and if you run into any issues at all we’d love to hear about it so we can improve the experience

Great, of no obvious problems lurking I'll crack on and let you know if it explodes!

You’re welcome!

Hi, still doing some experiments and just wondered if there is a way to run() a flow without blocking?

Hmm, I’m no expert but after asking around it seems if you want

flow.run

 to be non-blocking, you should use 

concurrent.futures

 or a threadpool to run the flow. https://docs.python.org/3/library/concurrent.futures.html

Thanks, will give that a go.