{"record":{"id":"e6516dfe22e2423a","repo":"sgl-project/sglang","slug":"unknown-weight-cache-transport-backend-name-r","errorCode":null,"errorMessage":"Unknown weight cache transport backend {name!r}","messagePattern":"Unknown weight cache transport backend (.+?)","errorType":"exception","errorClass":"RuntimeError","httpStatus":null,"severity":"error","filePath":"python/sglang/srt/weight_cache/transport.py","lineNumber":205,"sourceCode":"        self._raise_not_implemented()\n\n\ndef choose_daemon_transport_backend(\n    state_tensors: Mapping[str, Tuple[torch.Tensor, bool]],\n) -> WeightCacheTransportBackend:\n    if VmmFdTransportBackend.can_export_state(state_tensors):\n        logger.info(\"[weight_cache] Using transport backend: %s\", VMM_FD_BACKEND)\n        return VmmFdTransportBackend()\n    logger.info(\"[weight_cache] Using transport backend: %s\", TORCH_IPC_BACKEND)\n    return TorchIpcTransportBackend()\n\n\ndef get_client_transport_backend(name: Optional[str]) -> WeightCacheTransportBackend:\n    if name in (None, \"\", TORCH_IPC_BACKEND):\n        return TorchIpcTransportBackend()\n    if name == VMM_FD_BACKEND:\n        return VmmFdTransportBackend()\n    raise RuntimeError(f\"Unknown weight cache transport backend {name!r}\")\n","sourceCodeStart":187,"sourceCodeEnd":206,"githubUrl":"https://github.com/sgl-project/sglang/blob/0132848349585cfe6aae51c4941cbae872505f8a/python/sglang/srt/weight_cache/transport.py#L187-L206","documentation":"get_client_transport_backend received a name that is neither None/''/torch_ipc nor vmm_fd, so there is no registered transport backend with that name.","triggerScenarios":"Passing a typo'd backend string (e.g. 'torch-ipc', 'VMM_FD') via CLI flag or env var to the IpcModelLoader constructor or _fetch_from_cache.","commonSituations":"Typo in --weight-cache-transport-backend; config written for a different sglang version with renamed backends.","solutions":["Use 'torch_ipc' (default) or 'vmm_fd'","Check spelling/case of the backend name in your launch config"],"exampleFix":"# before\nget_client_transport_backend(\"torch-ipc\")\n# after\nget_client_transport_backend(\"torch_ipc\")","handlingStrategy":"type-guard","validationCode":"from sglang.srt.weight_cache.transport import TORCH_IPC_BACKEND, VMM_FD_BACKEND\nif name not in (None, '', TORCH_IPC_BACKEND, VMM_FD_BACKEND):\n    name = None","typeGuard":"def is_valid_backend(name):\n    return name in (None, '', 'torch_ipc', 'vmm_fd')","tryCatchPattern":null,"preventionTips":["Use exact backend names: torch_ipc or vmm_fd","Validate config strings at parse time"],"tags":["config","transport","invalid-argument"],"backgroundTag":"invalid-backend-name","analyzedSha":"0132848349585cfe6aae51c4941cbae872505f8a","analyzedAt":"2026-08-28T05:10:05.995Z","schemaVersion":2},"datasetVersion":"2026-08-28T06:17:29.519Z"}