3d7acd3957
* Workflow completion algorithm use periodic scheduled jobs to poll DB and determine when a workflow is finished. The problem with this approach is that if Mistral runs another iteration of such job too soon then running such jobs will create a big load on the system. If too late, then a workflow may be in RUNNING state for too long after all its tasks are completed. The current implementation tries to predict a delay with which the next job should run, based on a number of incompleted tasks. This approach was initially taken because we switched to a non-blocking transactional model (previously we locked the entire workflow execution graph in order to change a state of anything) and in this architecture, when we have parallel branches, i.e. parallel DB transactions, we can't make a consistent read from DB from neither of these transactions to make a reliable decision about whether the workflow is completed or not. Using periodic jobs was a solution. However, this approach has been proven to work unreliably because such a prediction about delay before the next job iteration doesn't work well on all variety of use cases that we have. This patch removes using periodic jobs in favor of using the "two transactions" approach when in the first transaction we handle action completion event (and task completion if it causes it) and in the second transaction, if a task is completed, we check if the workflow is completed. This approach guarantees that at least one of the "second" transactions in parallel branches will make needed consistent read from DB (i.e. will see the actuall state of all needed objects) to make the right decision. Closes-Bug: #1799382 Change-Id: I2333507503b3b8226c184beb0bd783e1dcfa397f
Team and repository tags
Mistral
Workflow Service for OpenStack cloud. This project aims to provide a mechanism to define tasks and workflows without writing code, manage and execute them in the cloud environment.
Project Resources
Mistral Official Documentation
Project status, bugs, and blueprints are tracked on Launchpad
CloudFlow: visualization tool for workflow executions on https://github.com/nokia/CloudFlow
Additional resources are linked from the project Wiki page
Apache License Version 2.0 http://www.apache.org/licenses/LICENSE-2.0
Release notes for the project can be found at: https://docs.openstack.org/releasenotes/mistral/