Description of problem:
When publishing a repository with large metadata file (such as the others.xml.gz file in rhel-7-server-rpms). The Pulp worker can consumes more than 3GB of RAM for a few minutes. After that, the memory is freed to normally usage which is ok.

When calculating the open-size of a metadata, Pulp opens the gzip file which loads the whole gzip file into the memory.

plugins/distributors/yum/metadata/repomd.py
---------------------------------------------------------------------
        if file_path.endswith('.gz'):

            open_size_element = ElementTree.SubElement(data_element, 'open-size')

            open_checksum_attributes = {'type': self.checksum_type}
            open_checksum_element = ElementTree.SubElement(data_element, 'open-checksum',
                                                           open_checksum_attributes)

            try:
                file_handle = gzip.open(file_path, 'r')   <============= Here

            except:
                # cannot have an else clause to the try without an except clause
                raise

            else:
                try:
                    content = file_handle.read()
                    open_size_element.text = str(len(content))
                    open_checksum_element.text = self.checksum_constructor(content).hexdigest()

                finally:
                    file_handle.close()
---------------------------------------------------------------------

This is not quite an issue if user is syncing only a few repos. In the case of Satellite, user may sync large repositories at the same time, such as the Optimized Capsule sync. If one Capsule has 8 workers and each worker consumes 4GB+ of memory then the Capsule will run out of memory.


Steps to Reproduce:
1. Set Pulp to use only 1 worker so that we can monitor the progress easily.
2. Force full publish a rhel-7-server-rpms repository.
3. Use the following command to monitor the memory usage.

watch 'ps -aux | grep reserved_resource_worker-0'

4. The high memory consumption happens when Pulp finalizing the others.xml.gz file. You can use the following command to monitor the pulp working directory.

cd /var/cache/pulp/reserved_resource_worker-0@<satellite fqdn>/<pulp task id>/
watch 'ls -alrth'