{"record":{"id":"0c7f8df5c437090a","repo":"sgl-project/sglang","slug":"pd-decode-dcp-currently-requires-chunk-cache-en","errorCode":null,"errorMessage":"PD decode DCP currently requires chunk cache; --enable-hierarchical-cache is not supported.","messagePattern":"PD decode DCP currently requires chunk cache; --enable-hierarchical-cache is not supported\\.","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"python/sglang/srt/arg_groups/pd_disaggregation_hook.py","lineNumber":69,"sourceCode":"        # Fake transfer moves no KV and is only used for synthetic decode\n        # benchmarks, so it does not need the DCP relayout from Mooncake/NIXL.\n        if cfg.disaggregation_transfer_backend not in (\n            \"mooncake\",\n            \"nixl\",\n            \"fake\",\n        ):\n            raise ValueError(\n                \"PD decode DCP requires --disaggregation-transfer-backend \"\n                \"mooncake, nixl, or fake for synthetic benchmarking, got \"\n                f\"{cfg.disaggregation_transfer_backend!r}.\"\n            )\n        if cfg.disaggregation_decode_enable_radix_cache:\n            raise ValueError(\n                \"PD decode DCP currently requires chunk cache; \"\n                \"--disaggregation-decode-enable-radix-cache is not supported.\"\n            )\n        if cfg.enable_hierarchical_cache:\n            raise ValueError(\n                \"PD decode DCP currently requires chunk cache; \"\n                \"--enable-hierarchical-cache is not supported.\"\n            )\n\n    if cfg.disaggregation_mode == \"decode\":\n        if cfg.disaggregation_decode_enable_radix_cache:\n            if cfg.enable_hisparse:\n                raise ValueError(\n                    \"--disaggregation-decode-enable-radix-cache is incompatible \"\n                    \"with --enable-hisparse\"\n                )\n            if cfg.disaggregation_transfer_backend == \"fake\":\n                raise ValueError(\n                    \"--disaggregation-decode-enable-radix-cache is incompatible \"\n                    \"with --disaggregation-transfer-backend fake\"\n                )\n            if cfg.speculative_algorithm is not None:\n                raise ValueError(","sourceCodeStart":51,"sourceCodeEnd":87,"githubUrl":"https://github.com/sgl-project/sglang/blob/0132848349585cfe6aae51c4941cbae872505f8a/python/sglang/srt/arg_groups/pd_disaggregation_hook.py#L51-L87","documentation":"PD decode DCP requires chunk cache, so hierarchical cache (--enable-hierarchical-cache) is incompatible with it: HiCache layers KV across media with a layout DCP's relayout cannot handle.","triggerScenarios":"Enabling PD decode DCP together with --enable-hierarchical-cache.","commonSituations":"Combining hierarchical cache (for local KV reuse across restarts) with DCP on decode nodes in a disaggregated cluster.","solutions":["Disable --enable-hierarchical-cache on decode nodes using DCP","Or drop DCP if hierarchical cache is a hard requirement"],"exampleFix":"# before\n<DCP flags> --enable-hierarchical-cache\n# after\n<DCP flags>","handlingStrategy":"validation","validationCode":"if dcp_enabled:\n    cfg.enable_hierarchical_cache = False","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Document which features DCP excludes in your cluster runbooks"],"tags":["sglang","pd-disaggregation","dcp","hierarchical-cache","config-conflict"],"backgroundTag":"feature-incompatibility","analyzedSha":"0132848349585cfe6aae51c4941cbae872505f8a","analyzedAt":"2026-08-28T05:10:05.995Z","schemaVersion":2},"datasetVersion":"2026-08-28T06:17:29.519Z"}