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From Ragunathan Mariappan <mragunat...@gmail.com>
Subject Doubt about Asynchronous & Synchronous actions & workflow job waiting
Date Tue, 04 Oct 2011 10:26:11 GMT
Hi



I seem to comprehend different meanings for actions being synchronous and
Asynchronous based on the different sections of the documentations. Could
you help clarify?



1) Section 3.2.1.2 of 'Workflow Functional Specification' says that if an
action is *Asynchronous*, then the workflow job has to wait until the
computation/processing task completes before transitioning to the following
node in the workflow. And other way if the actions are Synchronous(FS
Action).



2) Section 3.3.4 of 'Workflow Functional Specification' & the section
'Introduction' of 'Writing a Custom Action Executor' says that if an action
is *Synchronous*(say FS Action), then the workflow job will wait until the
specified file commands are completed before continuing to the next action.



Thus 1 & 2 seems confusing as its mentioned that 'the workflow job waits'
for both Synchronous and Asynchronous actions to complete. Maybe I'm missing
something here.



---


Here are the excerpts from the documentation for your quick reference:



**

*3.2.1.2 Actions Are Asynchronous*



All computation/processing tasks triggered by an action node are executed *
asynchronously *by Oozie. For most types of computation/processing tasks
triggered by workflow action, *the workflow job has to wait until the
computation/processing task completes before transitioning to the following
node in the workflow.*



The *exception* is the fs action that is handled as a *synchronous *action.



-----------



*3.2.4 Fs (HDFS) action*

...



The FS commands are executed *synchronously* from within the FS action, *the
workflow job will wait until the specified file commands are completed
before continuing to the next action*.



-----------



*Custom Action Nodes*

* *

*Introduction*



    * *Synchronous *Node - Sync nodes are executed inline by Oozie, *which
waits for completion of these nodes before proceeding*. Hence, these nodes
should almost never be used and are meant for lightweight tasks like
FileSystem move, mkdir, delete.

    * *Asynchronouse *Nodes - Oozie *starts asynchrnous nodes, and then
monitors the action being executed for completion*. This is done via a
callback from the action or Oozie polling for the action status.



-----------


Thanks,

Ragu

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