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tensorflow分布式训练的学习

参考这篇文章：

https://zhuanlan.zhihu.com/p/41473323

参考下面的资料：

Tensorflow在1.4版本中引入了tf.estimator.train_and_evaluate函数，用来替换老版中Experiment类提供的功能。tf.estimator.train_and_evaluate简化了训练、评估和导出Estimator模型的过程，抽象了模型分布式训练和评估的细节，使得同样的代码在本地与分布式集群上的行为一致。

本文简要介绍如何自定义Estimator模型并通过使用tf.estimator.train_and_evaluate完成训练和评估。

主要步骤：

构建自己的Estimator模型
定义在训练和测试过程中数据如何输入给模型
定义传递给tf.estimator.train_and_evaluate函数的训练、评估和导出的详述参数(TrainSpec and EvalSpec)
使用tf.estimator.train_and_evaluate训练并评估模型

我们使用的数据集是《DBPedia Ontology Classification Dataset》(可点击下载)，是从数据集DBpedia 2014中挑选的14个类别的互不重叠的本体（Company, EducationalInstitution, Artist, Athlete, OfficeHolder, MeanOfTransportation, Building, NaturalPlace, Village, Animal, Plant, Album, Film, WrittenWork），每个本体类别随机选择了40,000 个训练样本和5,000个测试样本。因此，总共有560,000个训练样本和70,000个测试样本。

模型代码

def my_model(features, labels, mode, params):
  sentence = features['sentence']
  # Get word embeddings for each token in the sentence
  embeddings = tf.get_variable(name="embeddings", dtype=tf.float32,
                               shape=[params["vocab_size"], FLAGS.embedding_size])
  sentence = tf.nn.embedding_lookup(embeddings, sentence) # shape:(batch, sentence_len, embedding_size)
  # add a channel dim, required by the conv2d and max_pooling2d method
  sentence = tf.expand_dims(sentence, -1) # shape:(batch, sentence_len/height, embedding_size/width, channels=1)

  pooled_outputs = []
  for filter_size in params["filter_sizes"]:
      conv = tf.layers.conv2d(
          sentence,
          filters=FLAGS.num_filters,
          kernel_size=[filter_size, FLAGS.embedding_size],
          strides=(1, 1),
          padding="VALID",
          activation=tf.nn.relu)
      pool = tf.layers.max_pooling2d(
          conv,
          pool_size=[FLAGS.sentence_max_len - filter_size + 1, 1],
          strides=(1, 1),
          padding="VALID")
      pooled_outputs.append(pool)
  h_pool = tf.concat(pooled_outputs, 3) # shape: (batch, 1, len(filter_size) * embedding_size, 1)
  h_pool_flat = tf.reshape(h_pool, [-1, FLAGS.num_filters * len(params["filter_sizes"])]) # shape: (batch, len(filter_size) * embedding_size)
  if 'dropout_rate' in params and params['dropout_rate'] > 0.0:
    h_pool_flat = tf.layers.dropout(h_pool_flat, params['dropout_rate'], training=(mode == tf.estimator.ModeKeys.TRAIN))
  logits = tf.layers.dense(h_pool_flat, FLAGS.num_classes, activation=None)

  optimizer = tf.train.AdagradOptimizer(learning_rate=params['learning_rate'])
  def _train_op_fn(loss):
    return optimizer.minimize(loss, global_step=tf.train.get_global_step())

  my_head = tf.contrib.estimator.multi_class_head(n_classes=FLAGS.num_classes)
  return my_head.create_estimator_spec(
    features=features,
    mode=mode,
    labels=labels,
    logits=logits,
    train_op_fn=_train_op_fn
  )

dataset

def input_fn(path_csv, path_vocab, shuffle_buffer_size, num_oov_buckets):
  vocab = tf.contrib.lookup.index_table_from_file(path_vocab, num_oov_buckets=num_oov_buckets)
  # Load csv file, one example per line
  dataset = tf.data.TextLineDataset(path_csv)
  # Convert line into list of tokens, splitting by white space; then convert each token to an unique id
  dataset = dataset.map(lambda line: parse_line(line, vocab))
  if shuffle_buffer_size > 0:
    dataset = dataset.shuffle(shuffle_buffer_size).repeat()
  dataset = dataset.batch(FLAGS.batch_size).prefetch(1)
  return dataset

训练

classifier = tf.estimator.Estimator(
    model_fn=my_model,
    params={
      'vocab_size': config["vocab_size"],
      'filter_sizes': map(int, FLAGS.filter_sizes.split(',')),
      'learning_rate': FLAGS.learning_rate,
      'dropout_rate': FLAGS.dropout_rate
    },
    config=tf.estimator.RunConfig(model_dir=FLAGS.model_dir, save_checkpoints_steps=FLAGS.save_checkpoints_steps)
  )

  train_spec = tf.estimator.TrainSpec(
    input_fn=lambda: input_fn(path_train, path_words, FLAGS.shuffle_buffer_size, config["num_oov_buckets"]),
    max_steps=FLAGS.train_steps
  )
  input_fn_for_eval = lambda: input_fn(path_eval, path_words, 0, config["num_oov_buckets"])
  eval_spec = tf.estimator.EvalSpec(input_fn=input_fn_for_eval, throttle_secs=300)


  tf.estimator.train_and_evaluate(classifier, train_spec, eval_spec)