Invalidating Jug Task Results (invalidate subcommand)

When you invalidate results of a task, you are telling jug that everything that was computed using that function should no longer be used. Thus, any result which depended on that function needs to be recomputed.

Invalidation is manual

To invalidate a task, you need to use the invalidate command. Jug does not detect that you fixed a bug in your code automatically.

Invalidation is dependency aware

When you invalidate a task, all results that depend on the invalid results will also be invalidated. This is what makes the invalidate subcommand so powerful.

Example

Consider the British parliament example we used elsewhere in this guide:

allcounts = []
for mp in MPs:
    article = get_data(mp)
    words = count_words(mp, article)
    allcounts.append(words)

global_counts = add_counts(allcounts) # Here all processes must sync

Its dependency graph looks like this:

M0 -> get_data -> count_words -> C0
M1 -> get_data -> count_words -> C1
M2 -> get_data -> count_words -> C2
...
C0 C1 C2 -> add_counts -> avgs
C0 + avgs -> divergence
C1 + avgs -> divergence
C2 + avgs -> divergence
...

This is a typical fan-in-fan-out structure. After you have run the code, jug status will give you this output:

\      Waiting       Ready    Finished     Running  Task name
----------------------------------------------------------------------------------
           0           0           1           0  jugfile.add_counts
           0           0         656           0  jugfile.count_words
           0           0         656           0  jugfile.divergence
           0           0         656           0  jugfile.get_data
..................................................................................
           0           0        1969           0  Total

Now assume that add_counts has a bug. Now you must:

  1. Fix the bug (well, of course)
  2. Rerun everything that could have been affected by the bug.

Jug invalidation helps you with the second task.

$ jug invalidate add_counts
Invalidated  Task name
-----------------------------------------------------------
           1  jugfile.add_counts
         656  jugfile.divergence
...........................................................
         657  Total

will remove results for all the add_counts tasks, and all the ``divergence`` tasks because those results depended on results from add_counts. Now, jug status gives us:

\     Waiting       Ready    Finished     Running  Task name
------------------------------------------------------------------------------------
           0           1           0           0  jugfile.add_counts
           0           0         656           0  jugfile.count_words
         656           0           0           0  jugfile.divergence
           0           0         656           0  jugfile.get_data
....................................................................................
         656           1        1312           0  Total

So, now when you run jug execute, add_counts will be re-run as will everything that could possibly have changed as well.