Benjamin Mahler created MESOS-8389:
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Summary: Notion of "removable" task in master code is inaccurate.
Key: MESOS-8389
URL: https://issues.apache.org/jira/browse/MESOS-8389
Project: Mesos
Issue Type: Improvement
Components: master
Reporter: Benjamin Mahler
In the past, the notion of a "removable" task meant: the task is terminal and
acknowledged. It appears now that a removable task is defined purely by its
state (terminal or unreachable) but not whether the terminal update is
acknowledged.
As a result, the code that is calling this function ({{isRemovable}}) ends up
being unintuitive. One example of a confusing piece of code is within
{{updateTask}}. Here, we have logic which says, if the task is removable,
recover the resources *but don't remove it*. This seems more intuitive if
directly described as: "if the task is no longer consuming resources, then
(e.g. transitioned to terminal or unreachable) then recover the resources".
If one looks up the documentation of {{isRemovable}}, it says "When a task
becomes removable, it is erased from the master's primary task data
structures", but that isn't accurate since this function doesn't say whether
the terminal task has been acknowledged, which is required for a task to be
removable.
I think an easy improvement here would be to move this notion of removable
towards something like {{isTerminalOrUnreachable}}. We could also think about
how to name this concept more generally, like {{canReleaseResources}} to
describe whether the task's resources are considered allocated.
If we do introduce a notion of {{isRemovable}}, it seems it should be saying
whether the task could be removed from the master, which includes checking that
terminal tasks have been acknowledged.
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