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Spark DL Inference Using External Frameworks

Example notebooks for the predict_batch_udf function (introduced in Spark 3.4).

Example Notebooks

The examples directory contains notebooks for each DL framework (based on their own published examples). The goal is to demonstrate how models trained and saved on single-node machines can be easily used for parallel inferencing in Spark clusters.

For example, a basic model trained in TensorFlow and saved on disk as "mnist_model" can be used in Spark as follows:

import numpy as np
from pyspark.sql.functions import predict_batch_udf
from pyspark.sql.types import ArrayType, FloatType

def predict_batch_fn():
    import tensorflow as tf
    model = tf.keras.models.load_model("/path/to/mnist_model")
    def predict(inputs: np.ndarray) -> np.ndarray:
        return model.predict(inputs)
    return predict

mnist = predict_batch_udf(predict_batch_fn,
                          return_type=ArrayType(FloatType()),
                          batch_size=1024,
                          input_tensor_shapes=[[784]])

df = spark.read.parquet("mnist_data")
predictions = df.withColumn("preds", mnist("data")).collect()

In this simple case, the predict_batch_fn will use TensorFlow APIs to load the model and return a simple predict function which operates on numpy arrays. The predict_batch_udf will automatically convert the Spark DataFrame columns to the expected numpy inputs.

All notebooks have been saved with sample outputs for quick browsing.

Running the Notebooks

If you want to run the notebooks yourself, please follow these instructions. For simplicity, this uses a small Spark Standalone cluster on a single host.

# clone repo and install sparkext
git clone https://github.com/leewyang/sparkext.git
cd sparkext

# install dependencies for example notebooks
# note: for PyTorch, you may need to follow instructions at: https://pytorch.org/get-started/locally/
cd examples
pip install -r requirements.txt

# setup environment variables
export SPARK_HOME=/path/to/spark
export MASTER=spark://$(hostname):7077
export SPARK_WORKER_INSTANCES=1
export CORES_PER_WORKER=8
export PYSPARK_DRIVER_PYTHON=jupyter
export PYSPARK_DRIVER_PYTHON_OPTS='lab'

# start spark standalone cluster
${SPARK_HOME}/sbin/start-master.sh; ${SPARK_HOME}/sbin/start-worker.sh -c ${CORES_PER_WORKER} -m 16G ${MASTER}

# start jupyter with pyspark
${SPARK_HOME}/bin/pyspark --master ${MASTER} \
--driver-memory 8G \
--executor-memory 8G \
--conf spark.python.worker.reuse=True

# BROWSE to localhost:8888 to view/run notebooks

# stop spark standalone cluster
${SPARK_HOME}/sbin/stop-worker.sh; ${SPARK_HOME}/sbin/stop-master.sh