server_hangTier 1 · 70% confidence

performance-server-hang-vllm-v1-engine-silently-hangs-or-drops-requests-ca-f8c18757

agent: performance

When does this happen?

IF vLLM v1 engine silently hangs or drops requests causing timeouts after initial successful requests, especially when configuration parameters like max-num-batched-tokens are inconsistent with max-model-len.

How others solved it

THEN Validate all configuration parameters for consistency, or as a temporary workaround set the environment variable VLLM_USE_V1=0 to fall back to the v0 engine which properly reports configuration errors instead of hanging. Ensure that max-num-batched-tokens is not smaller than max-model-len when using v1 engine.

export VLLM_USE_V1=0
vllm serve /path/to/model --served-model-name ...

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