{"record":{"id":"f4e6d9f465f71469","repo":"sgl-project/sglang","slug":"mooncake-s-batch-register-requires-a-newer-version","errorCode":null,"errorMessage":"Mooncake's batch register requires a newer version of mooncake-transfer-engine. Please upgrade Mooncake.","messagePattern":"Mooncake's batch register requires a newer version of mooncake-transfer-engine\\. Please upgrade Mooncake\\.","errorType":"exception","errorClass":"RuntimeError","httpStatus":null,"severity":"error","filePath":"python/sglang/srt/distributed/device_communicators/mooncake_transfer_engine.py","lineNumber":173,"sourceCode":"    def deregister(self, ptr):\n        try:\n            ret_value = self.engine.unregister_memory(ptr)\n        except Exception:\n            # Mark deregister as failed\n            ret_value = -1\n\n        if ret_value != 0:\n            logger.debug(\"Mooncake memory deregistration %s failed.\", ptr)\n\n    def batch_register(self, ptrs: List[int], lengths: List[int]) -> int:\n        \"\"\"Batch register multiple memory regions.\"\"\"\n        try:\n            ret_value = self.engine.batch_register_memory(ptrs, lengths)\n        except Exception:\n            # Mark batch register as failed\n            ret_value = -1\n            if not hasattr(self.engine, \"batch_register_memory\"):\n                raise RuntimeError(\n                    \"Mooncake's batch register requires a newer version of \"\n                    \"mooncake-transfer-engine. Please upgrade Mooncake.\"\n                )\n\n        if ret_value != 0:\n            logger.debug(\"Mooncake batch memory registration failed.\")\n        return ret_value\n\n    def batch_deregister(self, ptrs: List[int]) -> int:\n        \"\"\"Batch deregister multiple memory regions.\"\"\"\n        try:\n            ret_value = self.engine.batch_unregister_memory(ptrs)\n        except Exception:\n            # Mark batch deregister as failed\n            ret_value = -1\n\n        if ret_value != 0:\n            logger.debug(\"Mooncake batch memory deregistration failed.\")","sourceCodeStart":155,"sourceCodeEnd":191,"githubUrl":"https://github.com/sgl-project/sglang/blob/0132848349585cfe6aae51c4941cbae872505f8a/python/sglang/srt/distributed/device_communicators/mooncake_transfer_engine.py#L155-L191","documentation":"MooncakeTransferEngine.batch_register_memory registers many buffers at once by calling engine.batch_register_memory. Older mooncake-transfer-engine builds lack this method, so the call raises AttributeError, which is caught, and the code re-raises a RuntimeError telling you to upgrade when the attribute is missing. (If the method exists but fails, ret_value is -1 and it only logs a debug message instead.)","triggerScenarios":"Calling MooncakeTransferEngine.batch_register (public API) with an installed mooncake-transfer-engine version that does not expose TransferEngine.batch_register_memory — i.e. an older release than the one SGLang requires for batch registration.","commonSituations":"Running a new SGLang version (which uses batch registration for KV cache/HiCache) against a stale mooncake-transfer-engine pinned in the image or requirements; downgrading mooncake to work around another bug and hitting this; mixed-version clusters where only some nodes were upgraded.","solutions":["pip install mooncake-transfer-engine --upgrade to a version that includes batch_register_memory","Check the installed version: pip show mooncake-transfer-engine, and compare with SGLang's required minimum","If upgrading is impossible, pin/use an SGLang version compatible with your mooncake build"],"exampleFix":"# before\npip show mooncake-transfer-engine  # e.g. 0.2.x -> RuntimeError on batch_register\n\n# after\npip install mooncake-transfer-engine --upgrade\npython -c \"from mooncake.engine import TransferEngine; print(hasattr(TransferEngine, 'batch_register_memory'))\"  # True","handlingStrategy":"validation","validationCode":"from mooncake.engine import TransferEngine\nif not hasattr(TransferEngine, 'batch_register_memory'):\n    raise RuntimeError('mooncake too old for batch_register; upgrade mooncake-transfer-engine')","typeGuard":"def supports_batch_register(engine) -> bool:\n    return hasattr(engine.engine, 'batch_register_memory')","tryCatchPattern":"try:\n    eng.batch_register(...)\nexcept RuntimeError as e:\n    if 'upgrade Mooncake' in str(e):\n        # fall back to per-buffer register() calls or abort with upgrade hint\n        ...\n    raise","preventionTips":["Check hasattr(engine, 'batch_register_memory') before batch registration","Pin mooncake-transfer-engine to the minimum version SGLang requires","Verify version in container build: pip show mooncake-transfer-engine"],"tags":["mooncake","version-mismatch","batch-register","upgrade-required","sglang"],"backgroundTag":"library-version-mismatch","analyzedSha":"0132848349585cfe6aae51c4941cbae872505f8a","analyzedAt":"2026-08-28T05:10:05.995Z","schemaVersion":2},"datasetVersion":"2026-08-28T06:17:29.519Z"}