Propose queue changeTaskRunPriority

Author: lotas

README.md

@@ -68,4 +68,5 @@ See [mechanics](mechanics.md) for more detail.
 | RFC#180 | [Github cancel previous tasks](rfcs/0180-Github-cancel-previous-tasks.md)                                                                                                              |
 | RFC#182 | [Allow remote references to .taskcluster.yml files processed by Taskcluster-GitHub](rfcs/0182-taskcluster-yml-remote-references.md)                                                    |
 | RFC#189 | [Batch APIs for task definition, status and index path](rfcs/0189-batch-task-apis.md)                                                                                                  |
+| RFC#190 | [Queue change task run priority](rfcs/0190-queue-change-task-run-priority.md)                                                                                                          |
 | RFC#191 | [Worker Manager launch configurations](rfcs/0191-worker-manager-launch-configs.md)                                                                                                     |

rfcs/0190-queue-change-task-run-priority.md

@@ -0,0 +1,55 @@
+# RFC 0190 - Queue change task run priority
+* Comments: [#0190](https://github.com/taskcluster/taskcluster-rfcs/pull/190)
+* Proposed by: @lotas
+
+## Summary
+
+Since we refactored queue internals it became possible to see what tasks are pending for a particular
+worker pool / task queue.
+
+This RFC proposes new API method that would allow to change the priority of the existing task run.
+
+## Motivation
+
+There might be several use-cases when some worker pool has a lot of pending tasks and there is a need
+to move some more important task to the top of the waiting list, or also move down less important ones.
+
+Instead of cancelling existing tasks we can instead choose to change task run priorities.
+
+## Details
+
+I propose we implement this on a task run level and not the task itself:
+
+* tasks are supposed to be immutable
+* changing the priority makes more sense in the context of a specific run, not the whole task
+
+Queue service will expose new method `queue.changeTaskRunPriority(taskId, runId, newPriority)`.
+
+This will try to do the following:
+
+* update `task.runs[runId]` in the database to reflect priority change (possibly extra field to keep the original)
+* update `priority` field in the `queue_pending_tasks` table
+
+If any of this fails (for example task is being changed by some other process), this method will also fail.
+
+This will also require introduction of the new scopes (anyOf):
+
+* `queue:change-task-run-priority-in-queue:<taskQueueId>`
+* `queue:change-task-run-priority:<taskId>`
+
+
+Current order for picking up tasks is based on the task priority and insertion time (FIFO).
+This RFC proposes to change the priority only, and leave the insertion time as is.
+
+
+### Other considerations
+
+Chain of Trust validation might be broken if we change too much of the task definition or run.
+We need to make sure we don't break it with this change.
+
+
+
+
+## Implementation
+
+_pending_

rfcs/README.md

@@ -56,4 +56,5 @@
 | RFC#180 | [Github cancel previous tasks](0180-Github-cancel-previous-tasks.md)                                                                                                              |
 | RFC#182 | [Allow remote references to .taskcluster.yml files processed by Taskcluster-GitHub](0182-taskcluster-yml-remote-references.md)                                                    |
 | RFC#189 | [Batch APIs for task definition, status and index path](0189-batch-task-apis.md)                                                                                                  |
+| RFC#190 | [Queue change task run priority](0190-queue-change-task-run-priority.md)                                                                                                          |
 | RFC#191 | [Worker Manager launch configurations](0191-worker-manager-launch-configs.md)                                                                                                     |