Memoizing

Memoizing is similar to caching, however it only applies to steps within a run, and serves a subtly different purpose. With caching, a cache hit still results in a new step entity, but the result will be shared. Memoizing is more lightweight because the existing execution is referenced directly, rather than creating a new step which references the existing result.

Memoizing can be used as a way of optimizing runs (by sharing a result), and also to make debugging runs easier.

Enable memoizing of a task with the memo option:

@task(memo=True)
def fetch_user(user_id):
    ...

Memoized steps are indicated in Studio with a pin icon.

As with caching, explicitly clicking the 're-run' button for a step will force the step to be re-run, even if it's memoized. Then subsequent memoizing will use the new step execution.

If a step is manually re-run in a child workspace, the memoized results will be used (but memoized results from the child workspace aren't available to the parent). This follows the same rules as caching.

For debugging

Memoizing provides several benefits for debugging:

1. Memoizing a task with side effects (e.g., sending a notification email) means you can re-run the whole run (or part of it) without that side-effect happening.

2. Memoizing slow tasks allows you to fix bugs that are occurring elsewhere in the workflow.

This is particularly useful when re-running a workflow from a production workspace in a development workspace (assuming the production workspace is configured as an ancestor of the development workspace). By liberally memoizing tasks, specific steps can be re-run in the development workspace without re-running downstream steps.

For optimization

Memoizing can also be used as an optimization for workflows. For example, if a resource needs to be used in multiple parts of a workflow, rather than passing around that resource, the task to fetch it can be memoized:

@task(memo=True)
def fetch_user(user_id):
    ...

@task()
def send_email(user_id):
    user = fetch_user(user_id)
    ...

@task()
def send_notification(user_id):
    user = fetch_user(user_id)
    ...

In this case, the fetch_user task will only be executed once for the run, even if steps are re-run (provided the user ID doesn't change).

Memo parameters

As with caching, by default the memoization considers all arguments. This can be changed by specifying the individual parameters:

@task(memo=["machine_id"])
def apply_configuration(machine_id, config):
    ...

In this case, the function to apply configuration to a machine is only run once for the specified machine, regardless of whether the configuration itself changes. This can allow you to make changes to a workflow and re-run it with (some) confidence that a new configuration won't be applied.