gRPC 2 UNKNOWN vs 9 FAILED_PRECONDITION
Both gRPC 2 (UNKNOWN) and 9 (FAILED_PRECONDITION) belong to the gRPC Status Codes category. 2 indicates that an unknown error occurred. This may be returned when a server raises an exception that doesn't map to any known gRPC status code. Meanwhile, 9 means that the operation was rejected because the system is not in a state required for the operation's execution. For example, deleting a non-empty directory.
Description
An unknown error occurred. This may be returned when a server raises an exception that doesn't map to any known gRPC status code.
When You See It
The server threw an unhandled exception or returned an error that gRPC couldn't classify into a more specific status code.
How to Fix
Check the server logs for the underlying exception. Wrap server-side errors with explicit gRPC status codes instead of letting them bubble up as UNKNOWN.
Description
The operation was rejected because the system is not in a state required for the operation's execution. For example, deleting a non-empty directory.
When You See It
The request is valid on its own, but the system's current state doesn't allow it — like trying to delete a non-empty directory or update a resource that has been modified concurrently.
How to Fix
Bring the system into the required state before retrying. For example, empty the directory first, or re-read the resource to get the latest version before updating.
Key Differences
gRPC 2: An unknown error occurred. This may be returned when a server raises an exception that doesn't map to any known gRPC status code.
gRPC 9: The operation was rejected because the system is not in a state required for the operation's execution. For example, deleting a non-empty directory.
You encounter 2 when the server threw an unhandled exception or returned an error that gRPC couldn't classify into a more specific status code.
You encounter 9 when the request is valid on its own, but the system's current state doesn't allow it — like trying to delete a non-empty directory or update a resource that has been modified concurrently.
When to Use Which
For 2 (UNKNOWN): Check the server logs for the underlying exception. Wrap server-side errors with explicit gRPC status codes instead of letting them bubble up as UNKNOWN. For 9 (FAILED_PRECONDITION): Bring the system into the required state before retrying. For example, empty the directory first, or re-read the resource to get the latest version before updating.