Queue

Last updated on Oct 9, 2020

Introduction

Queue is a collection of PodGroups, which adopts FIFO. It is also used as the basis for resource division.

Example

apiVersion: scheduling.volcano.sh/v1beta1
kind: Queue
metadata:
  creationTimestamp: "2020-08-10T11:54:36Z"
  generation: 1
  name: default
  resourceVersion: "559"
  selfLink: /apis/scheduling.volcano.sh/v1beta1/queues/default
  uid: 14082e4c-bef6-4248-a414-1e06d8352bf0
spec:
  reclaimable: true
  weight: 1
  capability:
    cpu: "4"
    memory: "4096Mi"
status:
  state: Open

Key Fields

weight

weight indicates the relative weight of a queue in cluster resource division. The resource allocated to the queue equals (weight/total-weight) x total-resource. total-weight is the total weight of all queues. total-resource is the total number of cluster resources. weight is a soft constraint.

capability

capability indicates the upper limit of resources the queue can use. It is a hard constraint.

reclaimable

reclaimable specifies whether to allow other queues to reclaim extra resources occupied by a queue when the queue uses more resources than allocated. The default value is true.

Status

Open

Open indicates that the queue is available and can accept new PodGroups.

Closed

Closed indicates that the queue is unavailable and cannot accept any new PodGroups.

Closing

Closing indicates that the queue is becoming unavailable. It is a transient state. A Closing queue cannot accept any new PodGroups.

Unknown

Unknown indicates that the queue status is unknown because of unexpected situations such as network jitter.

Usage

Weight for Cluster Resource Division - 1

Preparations

  • A total of 4 CPUs in a cluster are available.
  • A queue with name set to default and weight set to 1 has been created by Volcano.
  • No running tasks are in the cluster.

Operation

  1. If no other queues are created, queue default can use all CPUs.
  2. Create queue test whose weight is 3. The CPU resource allocated to queue default changes to 1C and that allocated to queue test is 3C because weight(default):weight(test) equals 1:3.
  3. Create PodGroups p1 and p2, which belong to queues default and test, respectively.
  4. Create job j1 that has a CPU request of 1C in p1.
  5. Create job j2 that has a CPU request of 3C in p2.
  6. Check the status of j1 and j2. Both the jobs are running normally.

Weight for Cluster Resource Division - 2

Preparations

  • A total of 4 CPUs in a cluster are available.
  • A queue with name set to default and weight set to 1 has been created by Volcano.
  • No running tasks are in the cluster.

Operation

  1. If no other queues are created, queue default can use all CPUs.
  2. Create PodGroup p1 that belongs to queue default.
  3. Create job j1 with a CPU request of 1C and job j2 with a CPU request of 3C in p1. Both the jobs are running normally.
  4. Create queue test whose weight is 3. The CPU resource allocated to queue default changes to 1C and that allocated to queue test is 3C because weight(default):weight(test) equals 1:3. As no tasks in queue test, jobs in queue default can still run normally.
  5. Create PodGroup p2 that belongs to queue test.
  6. Create job j2 with a CPU request of 3C in p2. j2 will be evicted to return the resource to queue test.

Capability for Overuse of Resources

Preparations

  • A total of 4 CPUs in a cluster are available.
  • A queue with name set to default and weight set to 1 has been created by Volcano.
  • No running tasks are in the cluster.

Operation

  1. Create queue test whose capability is 2C.
  2. Create PodGroup p1 that belongs to queue test.
  3. Create job j1 that has a CPU request of 1C in p1. j1 runs normally.
  4. Create job j2 that has a CPU request of 3C in p1. j2 becomes pending because of the limit of capability.

Reclaimable for Resource Return

Preparations

  • A total of 4 CPUs in a cluster are available.
  • A queue with name set to default and weight set to 1 has been created by Volcano.
  • No running tasks are in the cluster.

Operation

  1. Create queue test whose reclaimable is false and weight is 1. The CPU resources allocated to queues default and test are both 2C.
  2. Create PodGroups p1 and p2, which belong to queues test and default, respectively.
  3. Create job j1 that has a CPU request of 3C in p1. j1 runs normally because there are no tasks in queue default.
  4. Create job j2 that has a CPU request of 2C in p2. The status of j2 is pending because reclaimable is set to false for queue test. Queue test will NOT return resources to other queues until some tasks in it are completed.

Note

default Queue

When Volcano starts, it automatically creates queue default whose weight is 1. Subsequent jobs that are not assigned to a queue will be assigned to queue default.

Soft Constraint About weight

weight determines the resources allocated to a queue, but not the upper limit. As per the preceding examples, a queue can use more resources than allocated when there are idle resources in other queues. This a good characteristic of Volcano and delivers a better cluster resource usage.