title: Connection pool is full warning while reading S3 objects via multiple threads
body: <p>I am using boto3 to read s3 objects</p>
  <pre><code>s3_client = boto3.client('s3', region_name='us-east-1')
  obj = s3_client.get_object(Bucket=S3_BUCKET, Key=key)
  </code></pre>
  <p>I am running this via 50-100 threads to access different objects and getting warning :</p>
  <blockquote>
  <p>urllib3.connectionpool - WARNING - Connection pool is full, discarding connection: s3.amazonaws.com</p>
  </blockquote>
  <p>How can I increase the connection pool size?</p>
  <p>Is there any better way to access different S3 objects with multiple threads?</p>