{"record":{"id":"562d787d51cd3f20","repo":"sgl-project/sglang","slug":"enable-linear-replayssm-is-not-supported-under-p","errorCode":null,"errorMessage":"--enable-linear-replayssm is not supported under PD disaggregation yet (follow-up). Got --disaggregation-mode={cfg.disaggregation_mode!r}.","messagePattern":"--enable-linear-replayssm is not supported under PD disaggregation yet \\(follow-up\\)\\. Got --disaggregation-mode=(.+?)\\.","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"python/sglang/srt/server_args.py","lineNumber":6956,"sourceCode":"                    f\"--linear-attn-decode-backend={decode!r}.\"\n                )\n            from sglang.srt.arg_groups.overrides import (\n                mamba_extra_buffer_of,\n            )\n\n            if mamba_extra_buffer_of(resolved_view(self)):\n                raise ValueError(\n                    \"--enable-linear-replayssm requires --mamba-radix-cache-strategy \"\n                    \"no_buffer (the default); the extra_buffer ping-pong \"\n                    \"donation path is not yet supported (follow-up). Got \"\n                    f\"--mamba-radix-cache-strategy={cfg.mamba_radix_cache_strategy!r}.\"\n                )\n            if cfg.disaggregation_mode != \"null\":\n                # The disaggregated decode pool (HybridMambaDecodeReqToTokenPool)\n                # is not wired for the ReplaySSM ring, so the flag would silently\n                # no-op there; disagg also runs a different cache/coordination\n                # flow that is not yet validated for ReplaySSM (follow-up).\n                raise ValueError(\n                    \"--enable-linear-replayssm is not supported under PD \"\n                    \"disaggregation yet (follow-up). Got \"\n                    f\"--disaggregation-mode={cfg.disaggregation_mode!r}.\"\n                )\n            if cfg.linear_replayssm_cache_len < 1:\n                raise ValueError(\n                    \"--linear-replayssm-cache-len must be >= 1, got \"\n                    f\"{cfg.linear_replayssm_cache_len}.\"\n                )\n\n        # ReplaySSM spec-verify (Part B of #28511): linear-chain target verify via\n        # fold-every-commit -- the verify stores each draft step's raw inputs into\n        # the per-slot (rawv, rawk, g, beta) window and the commit replays the\n        # accepted prefix into the fp32 checkpoint. The intra-window interaction\n        # uses a strictly-lower causal mask, so it is valid ONLY for a linear\n        # draft chain (speculative_eagle_topk in {None, 1}, i.e. NEXTN / MTP);\n        # EAGLE tree verify (topk > 1) must fall back to the recurrent verify.\n        # GDN sizes the window to the draft maximum; KDA (kda_backend) keeps a","sourceCodeStart":6938,"sourceCodeEnd":6974,"githubUrl":"https://github.com/sgl-project/sglang/blob/0132848349585cfe6aae51c4941cbae872505f8a/python/sglang/srt/server_args.py#L6938-L6974","documentation":"ReplaySSM is not yet supported under prefill/decode (PD) disaggregation: the disaggregated decode pool (HybridMambaDecodeReqToTokenPool) is not wired for the ReplaySSM ring and the disagg cache/coordination flow is unvalidated, so enabling it would silently no-op or misbehave. The check rejects any --disaggregation-mode other than null.","triggerScenarios":"--enable-linear-replayssm together with --disaggregation-mode prefill or decode.","commonSituations":"Enabling ReplaySSM on an existing PD-disaggregated deployment; adding disagg flags to a single-node ReplaySSM benchmark config.","solutions":["Run ReplaySSM without PD disaggregation: remove --disaggregation-mode (or set null)","Or remove --enable-linear-replayssm on disagg deployments until support lands (follow-up)"],"exampleFix":"# before\n--enable-linear-replayssm --disaggregation-mode decode\n# after\n--enable-linear-replayssm","handlingStrategy":"validation","validationCode":"def validate(disagg_mode, enable_replayssm):\n    return not enable_replayssm or disagg_mode == \"null\"","typeGuard":"def is_standalone(mode: str) -> bool: return mode == \"null\"","tryCatchPattern":null,"preventionTips":["Check feature support matrix before enabling experimental flags on disagg deployments","Keep disagg and single-node launch configs separate"],"tags":["sglang","replayssm","pd-disaggregation","unsupported-feature"],"backgroundTag":"unsupported-feature-combination","analyzedSha":"0132848349585cfe6aae51c4941cbae872505f8a","analyzedAt":"2026-08-28T05:10:05.995Z","schemaVersion":2},"datasetVersion":"2026-08-28T06:17:29.519Z"}