New -Wforce option for pbs_ralter to enforce changes to start/end/duration of a reservation.

Owned by Arun Grover (Deactivated)
Aug 05, 2020
2 min read

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Overview

The motivation behind this change is to allow admins to force a change in the start-time/end-time/duration of a reservation. This is needed for situations where some nodes in a running reservation are down they currently cannot extend the duration because the reservation cannot be reconfirmed with insufficient resources.

This option provides a way for Admins to override the decision scheduler takes and extend/move the reservation without caring about oversubscription. This obviously means that It is left up to the Admin to deal with the cases where resources are oversubscribed.


Interface changes:

  • pbs_ralter -Wforce option
  • A new "-Wforce" option is introduced to pbs_ralter command.
  • This option enforces the changes made to start-time, end-time or duration of the reservation. 
  • This option can only be used by an Admin (i.e. a user with Manager privileges) in PBS. If a non-admin user uses this option, the following error message is printed on console - 
    • "pbs_ralter: Unauthorized Request"
  • If this option is used with attributes of the reservation that cannot be changed (like resources), the following error message is printed on console - 
    • "pbs_ralter: No support for requested service"


Implementation Details:

PBS will try to do the right thing and much as possible. If let's say an admin uses '-Wforce' option with ralter on a confirmed reservation and scheduler is able to confirm this reservation on a different set of nodes without resulting in any oversubscription then the PBS server will use scheduler provided solution.

Cases, where the scheduler fails to reconfirm the ralter changes, will make the PBS server enforce it on the reservation (potentially resulting into oversubscription).

  • pbs_ralter when given with '-Wforce' option sends a request to the scheduler to confirm if the reservation can be confirmed with the new changes.
  • If the scheduler returns that the reservation can be confirmed then the changes take effect.
  • If the scheduler returns that the reservation cannot be confirmed then the server will check if '-Wforce' was requested in the ralter request. Once server knows it was a forced change, it will ignore scheduler's response and make the change to the reservation anyways.







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