DLLib Python Getting Start Guide#

1. Code initialization#

nncontext is the main entry for provisioning the dllib program on the underlying cluster (such as K8s or Hadoop cluster), or just on a single laptop.

It is recommended to initialize nncontext at the beginning of your program:

from bigdl.dllib.nncontext import *
sc = init_nncontext()

For more information about nncontext, please refer to nncontext

2. Distributed Data Loading#

Using Spark Dataframe APIs#

DLlib supports Spark Dataframes as the input to the distributed training, and as the input/output of the distributed inference. Consequently, the user can easily process large-scale dataset using Apache Spark, and directly apply AI models on the distributed (and possibly in-memory) Dataframes without data conversion or serialization

We create Spark session so we can use Spark API to load and process the data

spark = SQLContext(sc)
  1. We can use Spark API to load the data into Spark DataFrame, eg. read csv file into Spark DataFrame

    path = "pima-indians-diabetes.data.csv"

    If the feature column for the model is a Spark ML Vector. Please assemble related columns into a Vector and pass it to the model. eg.

    from pyspark.ml.feature import VectorAssembler
    vecAssembler = VectorAssembler(outputCol="features")
    vecAssembler.setInputCols(["num_times_pregrant", "plasma_glucose", "blood_pressure", "skin_fold_thickness", "2-hour_insulin", "body_mass_index", "diabetes_pedigree_function", "age"])
    assemble_df = vecAssembler.transform(df)
    assemble_df.withColumn("label", col("class").cast(DoubleType) + lit(1))
  2. If the training data is image, we can use DLLib api to load image into Spark DataFrame. Eg.

    imgPath = "cats_dogs/"
    imageDF = NNImageReader.readImages(imgPath, sc)

    It will load the images and generate feature tensors automatically. Also we need generate labels ourselves. eg:

    labelDF = imageDF.withColumn("name", getName(col("image"))) \
            .withColumn("label", getLabel(col('name')))

    Then split the Spark DataFrame into traing part and validation part

    (trainingDF, validationDF) = labelDF.randomSplit([0.9, 0.1])

3. Model Definition#

Using Keras-like APIs#

To define a model, you can use the Keras Style API.

x1 = Input(shape=[8])
dense1 = Dense(12, activation="relu")(x1)
dense2 = Dense(8, activation="relu")(dense1)
dense3 = Dense(2)(dense2)
dmodel = Model(input=x1, output=dense3)

After creating the model, you will have to decide which loss function to use in training.

Now you can use compile function of the model to set the loss function, optimization method.

dmodel.compile(optimizer = "adam", loss = "sparse_categorical_crossentropy")

Now the model is built and ready to train.

4. Distributed Model Training#

Now you can use ‘fit’ begin the training, please set the label columns. Model Evaluation can be performed periodically during a training.

  1. If the dataframe is generated using Spark apis, you also need set the feature columns. eg.

    model.fit(df, feature_cols=["features"], label_cols=["label"], batch_size=4, nb_epoch=1)

    Note: Above model accepts single input(column features) and single output(column label).

    If your model accepts multiple inputs(eg. column f1, f2, f3), please set the features as below:

    model.fit(df, feature_cols=["f1", "f2"], label_cols=["label"], batch_size=4, nb_epoch=1)

    Similarly, if the model accepts multiple outputs(eg. column label1, label2), please set the label columns as below:

    model.fit(df, feature_cols=["features"], label_cols=["l1", "l2"], batch_size=4, nb_epoch=1)
  2. If the dataframe is generated using DLLib NNImageReader, we don’t need set feature_cols, we can set transform to config how to process the images before training. Eg.

    from bigdl.dllib.feature.image import transforms
    transformers = transforms.Compose([ImageResize(50, 50), ImageMirror()])
    model.fit(image_df, label_cols=["label"], batch_size=1, nb_epoch=1, transform=transformers)

    For more details about how to use DLLib keras api to train image data, you may want to refer ImageClassification

5. Model saving and loading#

When training is finished, you may need to save the final model for later use.

BigDL allows you to save your BigDL model on local filesystem, HDFS, or Amazon s3.

  • save

    modelPath = "/tmp/demo/keras.model"
  • load

    loadModel = Model.loadModel(modelPath)
    preDF = loadModel.predict(df, feature_cols=["features"], prediction_col="predict")

You may want to refer Save/Load

6. Distributed evaluation and inference#

After training finishes, you can then use the trained model for prediction or evaluation.

  • inference

    1. For dataframe generated by Spark API, please set feature_cols and prediction_col

      dmodel.predict(df, feature_cols=["features"], prediction_col="predict")
    2. For dataframe generated by NNImageReader, please set prediction_col and you can set transform if needed

      model.predict(df, prediction_col="predict", transform=transformers)
  • evaluation

    Similary for dataframe generated by Spark API, the code is as below:

    dmodel.evaluate(df, batch_size=4, feature_cols=["features"], label_cols=["label"])

    For dataframe generated by NNImageReader:

    model.evaluate(image_df, batch_size=1, label_cols=["label"], transform=transformers)

7. Checkpointing and resuming training#

You can configure periodically taking snapshots of the model.

cpPath = "/tmp/demo/cp"

You can also set over_write to true to enable overwriting any existing snapshot files

After training stops, you can resume from any saved point. Choose one of the model snapshots to resume (saved in checkpoint path, details see Checkpointing). Use Models.loadModel to load the model snapshot into an model object.

loadModel = Model.loadModel(path)

8. Monitor your training#

  • Tensorboard

    BigDL provides a convenient way to monitor/visualize your training progress. It writes the statistics collected during training/validation. Saved summary can be viewed via TensorBoard.

    In order to take effect, it needs to be called before fit.

    dmodel.set_tensorboard("./", "dllib_demo")

    For more details, please refer visulization

9. Transfer learning and finetuning#

  • freeze and trainable

    BigDL DLLib supports exclude some layers of model from training.


    Layers that match the given names will be freezed. If a layer is freezed, its parameters(weight/bias, if exists) are not changed in training process.

    BigDL DLLib also support unFreeze operations. The parameters for the layers that match the given names will be trained(updated) in training process


    For more information, you may refer freeze

10. Hyperparameter tuning#

  • optimizer

    DLLib supports a list of optimization methods. For more details, please refer optimization

  • learning rate scheduler

    DLLib supports a list of learning rate scheduler. For more details, please refer lr_scheduler

  • batch size

    DLLib supports set batch size during training and prediction. We can adjust the batch size to tune the model’s accuracy.

  • regularizer

    DLLib supports a list of regularizers. For more details, please refer regularizer

  • clipping

    DLLib supports gradient clipping operations. For more details, please refer gradient_clip

11. Running program#

python you_app_code.py