Request rate limits enforcement policy

  • Article
  • 09/10/2024

Applies to: ✅ Azure Data Explorer

A workload group's request rate limits enforcement policy controls how request rate limits are enforced.

The policy object

A request rate limit policy has the following properties:

Name Supported values Default value Description
QueriesEnforcementLevel Cluster, QueryHead QueryHead Indicates the enforcement level for queries.
CommandsEnforcementLevel Cluster, Database Database Indicates the enforcement level for commands.

Request rate limits enforcement level

Request rate limits can be enforced at one of the following levels:

  • Cluster:
    • Rate limits are enforced by the single cluster admin node.
  • Database:
    • Rate limits are enforced by the database admin node that manages the database the request was sent to.
    • If there are multiple database admin nodes, the configured rate limit is effectively multiplied by the number of database admin nodes.
  • QueryHead:
    • Rate limits for queries are enforced by the query head node that the query was routed to.
    • This option affects queries that are sent with either strong or weak query consistency.
      • Strongly consistent queries run on the database admin node, and the configured rate limit is effectively multiplied by the number of database admin nodes.
      • For weakly consistent queries, the configured rate limit is effectively multiplied by the number of query head nodes.
    • This option doesn't apply to management commands.

Note

  • If the policy is undefined (null), the default enforcement level applies to both commands and queries.
  • Rate limits for cluster-scoped commands are always enforced at the cluster level, regardless of the value configured in the policy. For example: management commands that manage cluster-level policies.

Examples

Setup

  • The cluster has 10 nodes as follows:
    • one cluster admin node.
    • two database admin nodes (each manages 50% of the cluster's databases).
    • 50% of the tail nodes (5 out of 10) can serve as query heads for weakly consistent queries.
  • The default workload group is defined with the following policies: 
    "RequestRateLimitPolicies": [
    {
        "IsEnabled": true,
        "Scope": "WorkloadGroup",
        "LimitKind": "ConcurrentRequests",
        "Properties": {
            "MaxConcurrentRequests": 200
        }
    }
],
"RequestRateLimitsEnforcementPolicy": {
    "QueriesEnforcementLevel": "QueryHead",
    "CommandsEnforcementLevel": "Database"
}

Effective rate limits

The effective rate limits for the default workload group are:

  • The maximum number of concurrent cluster-scoped management commands is 200.
  • The maximum number of concurrent database-scoped management commands is
    2 (database admin nodes) x 200 (max per admin node) = 400.
  • The maximum number of concurrent strongly consistent queries is
    2 (database admin nodes) x 200 (max per admin node) = 400.
  • The maximum number of concurrent weakly consistent queries is
    5 (query heads) x 200 (max per query head) = 1000.

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