Bert Jansen (Microsoft) revealed some details on throttling when you access Microsoft 365 programmatically – via Microsoft Graph or CSOM and guided developers on how to regulate request traffic for optimized throughput using RateLimit headers (Here).
Demystifying SharePoint throttling
Throttling is necessary to ensure that no single user or application consumes too many resources compromising the stability of the entire system, which is used by many clients.
Throttling happens at
- User (there are user request limits. Microsoft counts all requests linked to user
- Application (Delegated or Application permissions)
- Resource units per app per minute
- Resource units per app per day
- Farm – Spike protection
Very common reason for throttling – when an Application (Delegated or Application permissions) reaches “Resource units per app per minute” threshold.
Usually you catch HTTP errors 429 or 503, wait for some time (respect Retry-after header) and try again.
SharePoint provides various APIs. Different APIs have different costs depending on the complexity of the API, but Microsoft favor Graph API over SharePoint REST/CSOM. The cost of APIs is normalized by SharePoint and expressed by resource units. Application’s limits are also defined using resource units.
Quota depends on tenant size.
Resource unit limits for an application in a tenant (please refer to the Microsoft article)
Predefined costs for Microsoft Graph calls: