Request rate limit policy (Preview)

• 01/18/2021
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The workload group's request rate limit policy lets you limit the number of concurrent requests classified into the workload group:

• Per workload group
• Per principal

The policy object

A request rate limit policy has the following properties:

Concurrent requests rate limit

A request rate limit of kind ConcurrentRequests includes the following property:

When a request exceeds the limit on maximum number of concurrent requests:

• The request's state, as presented by System information commands, will be Throttled.

• The error message will include the origin of the throttling and the capacity that's been exceeded. For example:

  • Examples:

    1. A throttled .create table command, that was classified to the default workload group, which has a limit of 80 concurrent requests at the scope of the workload group:

       The control command was aborted due to throttling. Retrying after some backoff might succeed. CommandType: 'TableCreate', Capacity: 80, Origin: 'RequestRateLimitPolicy/WorkloadGroup/default'.
       

    2. A throttled query, that was classified to a workload group named MyWorkloadGroup, which has a limit of 80 concurrent requests at the scope of the workload group:

       The query was aborted due to throttling. Retrying after some backoff might succeed. Capacity: 50, Origin: 'RequestRateLimitPolicy/WorkloadGroup/MyWorkloadGroup'.
       

    3. A throttled query, that was classified to a workload group named MyWorkloadGroup, which has a limit of 10 concurrent requests at the scope of a principal:

       The query was aborted due to throttling. Retrying after some backoff might succeed. Capacity: 10, Origin: 'RequestRateLimitPolicy/WorkloadGroup/MyWorkloadGroup/Principal/aaduser=9e04c4f5-1abd-48d4-a3d2-9f58615b4724;6ccf3fe8-6343-4be5-96c3-29a128dd9570'.
       

• The HTTP response code will be 429. The subcode will be TooManyRequests.

• The exception type will be QueryThrottledException for queries, and ControlCommandThrottledException for control commands.

Resource utilization rate limit

A request rate limit of kind ResourceUtilization includes the following properties:

When a request exceeds the limit on resources utilization:

• The request's state, as presented by System information commands, will be Throttled.

• The error message will include the the origin of the throttling and the quota that's been exceeded. For example:

  • Examples:

    1. A throttled request, that was classified to a workload group named Automated Requests, which has a limit of 10000 requests per day at the scope of a principal:

       The request was denied due to exceeding quota limitations. Resource: 'RequestCount', Quota: '10000', TimeWindow: '1.00:00:00', Origin: 'RequestRateLimitPolicy/WorkloadGroup/Automated Requests/Principal/aadapp=9e04c4f5-1abd-48d4-a3d2-9f58615b4724;6ccf3fe8-6343-4be5-96c3-29a128dd9570'.
       

    2. A throttled request, that was classified to a workload group named Automated Requests, which has a limit of 20000 total CPU seconds per day at the scope of the workload group:

       The request was denied due to exceeding quota limitations. Resource: 'TotalCpuSeconds', Quota: '20000', TimeWindow: '1.00:00:00', Origin: 'RequestRateLimitPolicy/WorkloadGroup/Automated Requests'.
       

• The HTTP response code will be 429. The subcode will be TooManyRequests.

• The exception type will be QuotaExceededException.

Example

The following policies allow up to:

• 500 concurrent requests for the workload group.
• 25 concurrent requests per principal.
• 50 requests per principal per hour.

[
  {
    "IsEnabled": true,
    "Scope": "WorkloadGroup",
    "LimitKind": "ConcurrentRequests",
    "Properties": {
      "MaxConcurrentRequests": 500
    }
  },
  {
    "IsEnabled": true,
    "Scope": "Principal",
    "LimitKind": "ConcurrentRequests",
    "Properties": {
      "MaxConcurrentRequests": 25
    }
  },
  {
    "IsEnabled": true,
    "Scope": "Principal",
    "LimitKind": "ResourceUtilization",
    "Properties": {
      "ResourceKind": "RequestCount",
      "MaxUtilization": 50,
      "TimeWindow": "01:00:00"
    }
  }
]

The default workload group

The default workload group has the following policy defined by default. This policy can be altered.

[
  {
    "IsEnabled": true,
    "Scope": "WorkloadGroup",
    "LimitKind": "ConcurrentRequests",
    "Properties": {
      "MaxConcurrentRequests": < Cores-Per-Node x 10 >
    }
  }
]

Notes

• The limit on maximum concurrent requests for the default workload group depends on the SKU of the cluster, and is calculated as: Cores-Per-Node x 10.
  • For example: A cluster that's set-up with Azure D14_v2 nodes, where each node has 16 vCores, will have the default limit of 16 x 10 = 160.
• If a workload group has no limit on maximum concurrent requests defined, then the maximum allowed value of 10000 applies.
• When altering the policy for the default workload group, there must be a limit defined for the workload group's max concurrent requests.
• The cluster's capacity policy may also limit the request rate of requests that fall under a specific category, for example: ingestions.
  • If either of the limits defined by capacity policy or by a request rate limit policy is exceeded, a control command will be throttled.
• When request rate limits of kind ConcurrentRequests are applied, the output of .show capacity may change based on those limits.
  • .show capacity will show the capacities for the principal that ran the request, according to the context of the request, the workload group it was classified into, and its effective policies.
  • Different principals may see different outputs when running the command, if their requests are classified into different workload groups.
  • When running .show capacity with(scope=cluster), the request context is ignored, and the output is only affected by the cluster's capacity policy.

Control commands

Manage the workload group's request concurrency policy with Workload groups control commands.