Caching model downloads from TF Hub

Overview

The tensorflow_hub library currently supports two modes for downloading models. By default, a model is downloaded as a compressed archive and cached on disk. Secondly, models can directly be read from remote storage into TensorFlow. Either way, the calls to tensorflow_hub functions in the actual Python code can and should continue to use the canonical tfhub.dev URLs of models, which are portable across systems and navigable for documentation. In the rare case that user code needs the actual filesystem location (after downloading and decompressing, or after resolving a model handle into a filesystem path), it can be obtained by the function hub.resolve(handle).

Caching of compressed downloads

The tensorflow_hub library by default caches models on the filesystem when they have been downloaded from tfhub.dev (or other hosting sites) and decompressed. This mode is recommended for most environments, except if disk space is scarce but network bandwidth and latency are superb.

The download location defaults to a local temporary directory but can be customized by setting the environment variable TFHUB_CACHE_DIR (recommended) or by passing the command-line flag --tfhub_cache_dir. The default cache location /tmp/tfhub_modules (or whatever os.path.join(tempfile.gettempdir(), "tfhub_modules") is evaluated to) should work in most cases.

Users who prefer persistent caching across system reboots can instead set TFHUB_CACHE_DIR to a location in their home directory. For example, a user of the bash shell on a Linux system can add a line like the following to ~/.bashrc:

export TFHUB_CACHE_DIR=$HOME/.cache/tfhub_modules

...restart the shell, and then this location will be used. When using a persistent location, be aware that there is no automatic cleanup.

Reading from remote storage

Users can instruct the tensorflow_hub library to directly read models from remote storage (GCS) instead of downloading the models locally with:

os.environ["TFHUB_MODEL_LOAD_FORMAT"] = "UNCOMPRESSED"

or by setting the command-line flag --tfhub_model_load_format to UNCOMPRESSED. This way, no caching directory is needed, which is especially helpful in environments that provide little disk space but a fast internet connection.

Running on TPU in Colab notebooks

On colab.research.google.com, downloading compressed models will conflict with the TPU runtime since the computation workload is delegated to another machine that does not have access to the cache location by default. There are two workarounds for this situation:

1) Use a GCS bucket that the TPU worker can access

The easiest solution is to instruct the tensorflow_hub library to read the models from TF Hub's GCS bucket as explained above. Users with their own GCS bucket can instead specify a directory in their bucket as the cache location with code like:

import os
os.environ["TFHUB_CACHE_DIR"] = "gs://my-bucket/tfhub-modules-cache"

...before calling the tensorflow_hub library.

2) Redirect all reads through the Colab host

Another workaround is to redirect all reads (even of large variables) through the Colab host:

load_options =
tf.saved_model.LoadOptions(experimental_io_device='/job:localhost')
reloaded_model = hub.load("https://tfhub.dev/...", options=load_options)

Note: See more information regarding valid handles here.

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