Request rate limit policy

  • Article

Applies to: ✅ Azure Data Explorer

The workload group's request rate limit policy lets you limit the number of concurrent requests classified into the workload group, per workload group or per principal.

Rate limits are enforced at the level defined by the workload group's Request rate limits enforcement policy.

The policy object

A request rate limit policy has the following properties:

Name Supported values Description
IsEnabled true, false Indicates if the policy is enabled or not.
Scope WorkloadGroup, Principal The scope to which the limit applies.
LimitKind ConcurrentRequests, ResourceUtilization The kind of the request rate limit.
Properties Property bag Properties of the request rate limit.

Concurrent requests rate limit

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

Name Type Description Supported Values
MaxConcurrentRequests int The maximum number of concurrent requests. [0, 10000]

Note

  • If a workload group doesn't have a specified limit on the maximum concurrent requests, it's subject to the default maximum value of 10000.

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.

The following table shows a few examples of concurrent requests that exceed the maximum limit and the error message that these requests return:

Scenario Error message
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 management command was aborted due to throttling. Retrying after some backoff might succeed. CommandType: 'TableCreate', Capacity: 80, Origin: 'RequestRateLimitPolicy/WorkloadGroup/default'.
A throttled query that was classified to a workload group named MyWorkloadGroup, which has a limit of 50 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'.
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 management commands.

Note

  • If either of the limits defined by the capacity policy or by a request rate limit policy is exceeded, a management command will be throttled.
  • The capacity policy may limit the request rate of requests that fall under a specific category, such as ingestions.

Resource utilization rate limit

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

Name Type Description Supported Values
ResourceKind ResourceKind The resource to limit.

When ResourceKind is TotalCpuSeconds, the limit is enforced based on post-execution reports of CPU utilization of completed requests. Requests that report utilization of 0.005 seconds of CPU or lower aren't counted. The limit (MaxUtilization) represents the total CPU seconds that can be consumed by requests within a specified time window (TimeWindow). For example, a user running ad-hoc queries may have a limit of 1000 CPU seconds per hour. If this limit is exceeded, subsequent queries will be throttled, even if started concurrently, as the cumulative CPU seconds have surpassed the defined limit within the sliding window period.		 RequestCount, TotalCpuSeconds
MaxUtilization long The maximum of the resource that can be utilized. RequestCount: [1, 16777215]; TotalCpuSeconds: [1, 828000]
TimeWindow timespan The sliding time window during which the limit is applied. [00:01:00, 1.00:00:00]

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 origin of the throttling and the quota that's been exceeded. For example:

The following table shows a few examples of requests that exceed the resource utilization rate limit and the error message that these requests return:

Scenario Error message
A throttled request that was classified to a workload group named Automated Requests, which has a limit of 1000 requests per hour at the scope of a principal. The request was denied due to exceeding quota limitations. Resource: 'RequestCount', Quota: '1000', TimeWindow: '01:00:00', Origin: 'RequestRateLimitPolicy/WorkloadGroup/Automated Requests/Principal/aadapp=9e04c4f5-1abd-48d4-a3d2-9f58615b4724;6ccf3fe8-6343-4be5-96c3-29a128dd9570'.
A throttled request, that was classified to a workload group named Automated Requests, which has a limit of 2000 total CPU seconds per hour at the scope of the workload group. The request was denied due to exceeding quota limitations. Resource: 'TotalCpuSeconds', Quota: '2000', TimeWindow: '01:00:00', Origin: 'RequestRateLimitPolicy/WorkloadGroup/Automated Requests'.
  • The HTTP response code will be 429. The subcode will be TooManyRequests.
  • The exception type will be QuotaExceededException.

How consistency affects rate limits

With strong consistency, the default limit on maximum concurrent requests 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 a default limit of 16 x 10 = 160.

With weak consistency, the effective default limit on maximum concurrent requests depends on the SKU of the cluster and number of query heads, and is calculated as: Cores-Per-Node x 10 x Number-Of-Query-Heads. For example, a cluster that's set up with Azure D14_v2 and 5 query heads, where each node has 16 vCores, will have an effective default limit of 16 x 10 x 5 = 800.

For more information, see Query consistency.

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 >
    }
  }
]

Note

  • When you alter the policy for the default workload group, a limit must be defined for the maximum concurrent requests.

Examples

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 following policies will block all requests classified to the workload group:

[
  {
    "IsEnabled": true,
    "Scope": "WorkloadGroup",
    "LimitKind": "ConcurrentRequests",
    "Properties": {
      "MaxConcurrentRequests": 0
    }
  },
]

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