Amazon SageMaker
Developer Guide

Run a Warm Start Hyperparameter Tuning Job

Use warm start to start a hyperparameter tuning job using one or more previous tuning jobs as a starting point. The results of previous tuning jobs are used to inform which combinations of hyperparameters to search over in the new tuning job. Hyperparameter tuning uses either Bayesian or random search to choose combinations of hyperparameter values from ranges that you specify. For more information, see How Hyperparameter Tuning Works. Using information from previous hyperparameter tuning jobs can help increase the performance of the new hyperparameter tuning job by making the search for the best combination of hyperparameters more efficient.

Note

Warm start tuning jobs typically take longer to start than standard hyperparameter tuning jobs, because the results from the parent jobs have to be loaded before the job can start. The increased time depends on the total number of training jobs launched by the parent jobs.

Reasons you might want to consider warm start include:

  • You want to gradually increase the number of training jobs over several tuning jobs based on the results you see after each iteration.

  • You get new data, and want to tune a model using the new data.

  • You want to change the ranges of hyperparameters that you used in a previous tuning job, change static hyperparameters to tunable, or change tunable hyperparameters to static values.

  • You stopped a previous hyperparameter job early or it stopped unexpectedly.

Types of Warm Start Tuning Jobs

There are two different types of warm start tuning jobs:

IDENTICAL_DATA_AND_ALGORITHM

The new hyperparameter tuning job uses the same input data and training image as the parent tuning jobs. You can change the hyperparameter ranges to search and the maximum number of training jobs that the hyperparameter tuning job launches. You can also change hyperparameters from tunable to static, and from static to tunable, but the total number of static plus tunable hyperparameters must remain the same as it is in all parent jobs. You cannot use a new version of the training algorithm, unless the changes in the new version do not affect the algorithm itself. For example, changes that improve logging or adding support for a different data format are allowed.

Use identical data and algorithm when you use the same training data as you used in a previous hyperparameter tuning job, but you want to increase the total number of training jobs or change ranges or values of hyperparameters.

When you run an warm start tuning job of type IDENTICAL_DATA_AND_ALGORITHM, there is an additional field in the response to DescribeHyperParameterTuningJob named OverallBestTrainingJob. The value of this field is the TrainingJobSummary for the training job with the best objective metric value of all training jobs launched by this tuning job and all parent jobs specified for the warm start tuning job.

TRANSFER_LEARNING

The new hyperparameter tuning job can include input data, hyperparameter ranges, maximum number of concurrent training jobs, and maximum number of training jobs that are different than those of its parent hyperparameter tuning jobs. You can also change hyperparameters from tunable to static, and from static to tunable, but the total number of static plus tunable hyperparameters must remain the same as it is in all parent jobs. The training algorithm image can also be a different version from the version used in the parent hyperparameter tuning job. When you use transfer learning, changes in the dataset or the algorithm that significantly affect the value of the objective metric might reduce the usefulness of using warm start tuning.

Warm Start Tuning Restrictions

The following restrictions apply to all warm start tuning jobs:

  • A tuning job can have a maximum of 5 parent jobs, and all parent jobs must be in a terminal state (Completed, Stopped, or Failed) before you start the new tuning job.

  • The objective metric used in the new tuning job must be the same as the objective metric used in the parent jobs.

  • The total number of static plus tunable hyperparameters must remain the same between parent jobs and the new tuning job. Because of this, if you think you might want to use a hyperparameter as tunable in a future warm start tuning job, you should add it as a static hyperparameter when you create a tuning job.

  • The type of each hyperparameter (continuous, integer, categorical) must not change between parent jobs and the new tuning job.

  • The number of total changes from tunable hyperparameters in the parent jobs to static hyperparameters in the new tuning job, plus the number of changes in the values of static hyperparameters cannot be more than 10. Each value in a categorical hyperparameter counts against this limit. For example, if the parent job has a tunable categorical hyperparameter with the possible values red and blue, you change that hyperparameter to static in the new tuning job, that counts as 2 changes against the allowed total of 10. If the same hyperparameter had a static value of red in the parent job, and you change the static value to blue in the new tuning job, it also counts as 2 changes.

  • Warm start tuning is not recursive. For example, if you create MyTuningJob3 as a warm start tuning job with MyTuningJob2 as a parent job, and MyTuningJob2 is itself an warm start tuning job with a parent job MyTuningJob1, the information that was learned when running MyTuningJob1 is not used for MyTuningJob3. If you want to use the information from MyTuningJob1, you must explicitly add it as a parent for MyTuningJob3.

  • The training jobs launched by every parent job in a warm start tuning job count against the 500 maximum training jobs for a tuning job.

  • Hyperparameter tuning jobs created before October 1, 2018 cannot be used as parent jobs for warm start tuning jobs.

Warm Start Tuning Sample Notebook

For a sample notebook that shows how to use warm start tuning, see https://github.com/awslabs/amazon-sagemaker-examples/blob/master/hyperparameter_tuning/image_classification_warmstart/hpo_image_classification_warmstart.ipynb. For instructions how to create and access Jupyter notebook instances that you can use to run the example in Amazon SageMaker, see Use Example Notebooks. Once you have created a notebook instance and opened it, select the SageMaker Examples tab to see a list of all the Amazon SageMaker samples. The warm start tuning example notebook is located in the Hyperparameter tuning section, and is named hpo_image_classification_warmstart.ipynb. To open a notebook, click on its Use tab and select Create copy.

Create a Warm Start Tuning Job

You can use either the low-level AWS SDK for Python (Boto 3) or the high-level Amazon SageMaker Python SDK to create a warm start tuning job.

Create a Warm Start Tuning Job ( Low-level Amazon SageMaker API for Python (Boto 3))

To use warm start tuning, you specify the values of a HyperParameterTuningJobWarmStartConfig object, and pass that as the WarmStartConfig field in a call to CreateHyperParameterTuningJob.

The following code shows how to create a HyperParameterTuningJobWarmStartConfig object and pass it to CreateHyperParameterTuningJob job by using the low-level Amazon SageMaker API for Python (Boto 3).

Create the HyperParameterTuningJobWarmStartConfig object:

warm_start_config = { "ParentHyperParameterTuningJobs" : [ {"HyperParameterTuningJobName" : 'MyParentTuningJob'} ], "WarmStartType" : "IdenticalDataAndAlgorithm" }

Create the warm start tuning job:

smclient = boto3.Session().client('sagemaker') smclient.create_hyper_parameter_tuning_job(HyperParameterTuningJobName = 'MyWarmStartTuningJob', HyperParameterTuningJobConfig = tuning_job_config, # See notebook for tuning configuration TrainingJobDefinition = training_job_definition, # See notebook for job definition WarmStartConfig = warm_start_config)

Create a Warm Start Tuning Job (Amazon SageMaker Python SDK)

To use the Amazon SageMaker Python SDK to run a warm start tuning job, you:

  • Specify the parent jobs and the warm start type by using a WarmStartConfig object.

  • Pass the WarmStartConfig object as the value of the warm_start_config argument of a HyperparameterTuner object.

  • Call the fit method of the HyperparameterTuner object.

For more information about using the Amazon SageMaker Python SDK for hyperparameter tuning, see https://github.com/aws/sagemaker-python-sdk#sagemaker-automatic-model-tuning.

This example uses an estimator that uses the Image Classification Algorithm algorithm for training. The following code sets the hyperparameter ranges that the warm start tuning job searches within to find the best combination of values. For information about setting hyperparameter ranges, see Define Hyperparameter Ranges.

hyperparameter_ranges = {'learning_rate': ContinuousParameter(0.0, 0.1), 'momentum': ContinuousParameter(0.0, 0.99)}

The following code configures the warm start tuning job by creating a WarmStartConfig object.

from sagemaker.tuner import WarmStartConfig, WarmStartTypes parent_tuning_job_name = "MyParentTuningJob" warm_start_config = WarmStartConfig(type=WarmStartTypes.IDENTICAL_DATA_AND_ALGORITHM, parents={parent_tuning_job_name})

Now set the values for static hyperparameters, which are hyperparameters that keep the same value for every training job that the warm start tuning job launches. In the following code, imageclassification is an estimator that was created previously.

imageclassification.set_hyperparameters(num_layers=18, image_shape='3,224,224', num_classes=257, num_training_samples=15420, mini_batch_size=128, epochs=30, optimizer='sgd', top_k='2', precision_dtype='float32', augmentation_type='crop')

Now create the HyperparameterTuner object and pass the WarmStartConfig object that you previously created as the warm_start_config argument.

tuner_warm_start = HyperparameterTuner(imageclassification, 'validation:accuracy', hyperparameter_ranges, objective_type='Maximize', max_jobs=10, max_parallel_jobs=2, base_tuning_job_name='warmstart', warm_start_config=warm_start_config)

Finally, call the fit method of the HyperparameterTuner object to launch the warm start tuning job.

tuner_warm_start.fit( {'train': s3_input_train, 'validation': s3_input_validation}, include_cls_metadata=False)