Add pyarrow to dependencies & Print warning on Ray import error (vllm…

…-project#1094)

requirements.txt

@@ -2,6 +2,7 @@ ninja  # For faster builds.
 psutil
 ray >= 2.5.1
 pandas  # Required for Ray data.
+pyarrow  # Required for Ray data.
 sentencepiece  # Required for LLaMA tokenizer.
 numpy
 torch >= 2.0.0

vllm/engine/ray_utils.py

@@ -2,6 +2,9 @@
 from typing import Optional, Tuple, TYPE_CHECKING
 
 from vllm.config import ParallelConfig
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
 
 try:
     import ray
@@ -28,7 +31,10 @@ def execute_method(self, method, *args, **kwargs):
             executor = getattr(self, method)
             return executor(*args, **kwargs)
 
-except ImportError:
+except ImportError as e:
+    logger.warning(f"Failed to import Ray with {e!r}. "
+                   "For distributed inference, please install Ray with "
+                   "`pip install ray pandas pyarrow`.")
     ray = None
     TorchDistributedWorker = None
     RayWorker = None  # pylint: disable=invalid-name