Request rate limit policy

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:

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.

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

• 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.

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 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:

• 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. With strong consistency, the default limit on maximum concurrent requests depends on the SKU of the eventhouse, and is calculated as: Cores-Per-Node x 10. For example, a eventhouse 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 eventhouse and number of query heads, and is calculated as: Cores-Per-Node x 10 x Number-Of-Query-Heads. For example, a eventhouse 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 >
    }
  }
]

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
    }
  },
]

Related content

• Workload groups
• Request rate limits enforcement policy
• .alter-merge workload_group command
• .create-or-alter workload_group command
• .drop workload_group command
• .show workload_group command