Hello everyone I have a question Is it possible to rerun onl

Question

Hello everyone I have a question Is it possible to rerun only a subset of the mapped tasks of a flow Like only the ones which have failed

Peter Roelants · Answer

Not that I know of However you might be able to use <https docs prefect io core concepts execution html triggers|Triggers> to only run a downstream task on failed tasks

Jitesh Khandelwal · Answer

I didn t understand how Triggers can be used here Below is a toy program I am working with Can you show an example of how a trigger can be used here ```import random import prefect from prefect import task Parameter Flow task def say world x if random random gt 5 1 0 return world format x task def say hello x return hello format x task def pliss print p logger = prefect context get logger <http logger info|logger info> format p with Flow param as flow p = Parameter roots default= A B C r1 = say world map p r2 = say hello map r1 pliss print map r2 if name == main flow run ```

Peter Roelants · Answer

What you could try ``` task trigger=prefect triggers any failed def pliss print p ```

Jitesh Khandelwal · Answer

This will ensure that `pliss print` will run even if the upstream task failed right

Jitesh Khandelwal · Answer

My goal is to somehow run only the branch that failed For example in the below flow if `say world A ` fails I want to restart just that and not `say world B and say world C ` ``` say world A say hello r1A pliss print r2A A B C say world B r1A r1B r1C say hello r1B r2A r2B r2C pliss print r2B say world C say hello r1C pliss print r2C ``` I tried to use results caching to achieve this but apparently caching doesn t work on mapped tasks I guess I am able to achieve this using some logic inside the task function to check if the task was already run before and if yes then raise a success signal

Peter Roelants · Answer

I think I misunderstood you before What about retrying the `say world` task at the point of failure e g ``` task max retries=5 retry delay=timedelta 0 def say world x ``` This should only restart a single task for a single mapped input it shouldn t restart the all mapped tasks afaik

Peter Roelants · Answer

Btw it should be possible to combine result caching with mapped tasks <https docs prefect io core advanced tutorials using results html mapping>

Jitesh Khandelwal · Answer

my use case is where the retries didn t help and someone will manually run later result caching of mapped tasks should be useful I ll check thanks +1