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RPC_S_MAX_CALLS_TOO_SMALL
The server concurrency value cannot support the requested registration mode
RPC_S_MAX_CALLS_TOO_SMALL concerns an RPC server’s maximum concurrent-call setting, not a count of failed client connections. Interface and server-listen registration APIs use call limits to size dispatch capacity; some registration modes reserve or require a minimum number of callable slots.
Trace the exact value supplied to interface registration and RpcServerListen-related setup, including whether the interface uses auto-listen. Do not simply set an extreme value: choose a limit consistent with worker capacity, memory use, call duration, and back-pressure design. If the value came from configuration, validate conversion and distinguish zero-as-default semantics from a literal zero.
What to inspect
- Log the max-calls value at every interface and server registration call.
- Check whether auto-listen or interface-specific limits change the minimum.
- Size application worker pools and RPC concurrency limits together.
References
- Microsoft: registering RPC interfaces
- Microsoft: maximum-call failures in dispatch
- Microsoft: RPC API reference
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